Will is still the captain of the Flying Dutchman. Nautical folklore and myths are not only very much real in the world of Pirates of the Caribbean, they're fundamentally part of the "natural order" of this universe. The Flying Dutchman ferrying souls lost at sea is part of this natural order and it's been well established in previous films that the Dutchman must have a Captain. Being the Dutchman's captain itself isn't a curse. The curse that Will has been freed from is the Captain's curse of not being allowed to step foot on land but once every 10 years. Now he can see his family whenever he wants. So why the Davy Jones nightmares? The universe needs a way to make sure that Will doesn't neglect his responsibility as the Dutchman's Captain since he can now step foot on land whenever he wants. Will is now being haunted by the ghost of Davy Jones as a reminder of what will happen to him if he doesn't ferry souls to the other side. Becoming a sea monster was also not part of the Dutchman's curse. Rather, it's karmic retribution for simply not doing the job.
Why is Jack down on his luck at the beginning of the film? Simple, it's because Angelica is using the Voodoo doll on him to get her revenge on him for marooning her and killing her father.
Furthermore, the witch that Barbossa visits in the film mentions "cursing his enemies." Jack may have more than one reason for his luck to have shifted so negatively.
It's somewhat poetic how Barbossa is giving Jack a taste of the same medicine he had in the first movie: according to one of his crew members in that movie, all his plans brought them from bad to worse.
In On Stranger Tides, Barbossa collected poisonous toads on his way to the Fountain. While he was also planning to use their poison to kill Blackbeard in that film, it was implied that he was just being "an older man with a hobby", suggesting that he showed interest in the biology of amphibious life. With that in mind, it makes perfect sense that his daughter would also be fond of scientific work.
Plus, Barbossa does have a mentality where it seems he's the only smart pirate around - although, to be fair, there have been signs since his original appearance that he's more intelligent than you would expect of a pirate, and he certainly seems to be more educated. note "I am disinclined to acquiesce to your request." Keep in mind that he wasn't just saying this with full knowledge of what it meant, he was also mocking Elizabeth's stilted attempts at parley. Barbossa is very sharp. So it's fitting when Carina interacts with the other pirates, she comes off as the most educated character.
How did the witch Barbossa hired get her hands on the compass? Think back to the last time we see the compass. Remember that rat that was sitting near the compass? It's only later we learn that rat is the witch's pet.
Borders on Fridge Horror, but there may be a reason Will started to become corrupted by the curse of the Flying Dutchman, even though he does love Elizabeth. It could be because along the way, he came upon some In-Universe Fridge Horror of his own. He realized that with time, Elizabeth would one day grow old and die, whilst he remained a lonely immortal. And one day, she would no longer be on that island waiting for him. So Will stopped seeing his condition as Cursed with Awesome, and more like an outright curse. Thankfully, by the end of the movie, Henry frees him from such a fate, so Will and Elizabeth will grow old and die together.
An alternate theory regarding the curse. Who was it who gave Davy Jones the Dutchman in the first place? Who charged him with The Duty? Who was it who described themselves as contrary, cruel and "untameable as the sea"? Calypso. And who was it who told said grouch sea-goddess her lover was the one who screwed her over in the first place? Calypso's getting back at Will breaking her heart by doing the same to him and Elizabeth.
The beginning parts of this movie show Jack in a sorry state indeed. He's more drunk than usual, "leading" his tiny crew from a docked ship, and has lost sight of himself so thoroughly that he's willing to trade the compass, which had been his most important possession, for a single bottle of rum. But then Henry finds him and pretty much says, "Don't tell me all the stories I heard about Captain Jack Sparrow were all lies." Which, of course, they weren't, because Henry Turner is standing right there, and likely wouldn't exist if not for Jack's exploits. Slowly, as the movie progresses, he starts to get tiny bits of his swagger back. By the end, though, he has the Pearl again and almost resembles the Captain Jack we originally came to know and love. And, perhaps not coincidentally, he met and helped take down the first foe he ever had as captain in the process - a feat that would have reminded Jack (assuming the flashback was accurate) of how he gained respect on the high seas as a pirate captain in the first place. Perhaps the movie wasn't hindered by Jack's less-than-awesome characterization. Perhaps Jack's rediscovery of himself and going from rock bottom to the person he once was, was at least part of the plot of the movie.
When you think about it, after killing Salazar, Barbossa, of all people - the FIRST Big Bad of the series - is at least in one way responsible for the defeats of his successors.
He piloted the Black Pearl into the Maelstrom in the third movie, allowing Will to kill Davy Jones.
Said ship, with the Flying Dutchman, was also able to sink the Endeavor and kill Lord Beckett. Barbossa even ordered the cannons to start firing.
He stabbed Blackbeard with his poisoned blade, and forced Jack to do the Profane Ritual with Blackbeard as the sacrifice.
The aforementioned killing of Salazar.
The film shows in several cases why Barbossa is a better person, and a better Captain for the Queen Anne's Revenge than her previous captain, Blackbeard.
Both rule with an iron fist over the seas, though Blackbeard also terrorizes his crew relentlessly, while Barbossa's men are proud to serve him, if still quite intimidated by his power. This healthier working relationship is also implied when Barbossa expresses some sadness when Salazar kills several of his crew members.
Both possess the ability to control ships, though Barbossa chooses to utilize his captured ships to make his own fleet rather than keep them as trophies, most likely due to the Black Pearl having been in such a situation before. Therefore, Barbossa's crew (or crews) take far more loot and are more successful than the crew working under Blackbeard.
Both end up saving their long-lost daughter's lives at the cost of their own. The main difference is that the selfish Blackbeard was tricked into drinking the wrong chalice and saving Angelica by Jack, while Barbossa genuinely loves Carina and willingly sacrifices his life for her.
Why would Barbossa still dislike Jack in this film (even referring to him as an enemy when talking to Salazar) when On Stranger Tides ended with the two on seemingly good terms? Seeing that Barbossa became the captain of the Revenge and learned how to trap and free the ships from the bottles between films, it's implied that he found out the Black Pearl was one of the ships Blackbeard captured, as he knows about it being trapped when confronting Jack at the wedding. It's likely, after finding out how the Sword of Triton worked, he wanted to try freeing the Pearl, only to find out that Jack and Gibbs had taken it from the ship before he took command. After all these years, they were still fighting over that ship.
As noted on the main page, every ship should have a member of the crew who knows how to navigate by the stars, which makes it weird that Carina and Barbossa are the only ones who know Jack who such a thing. The thing is, Jack's crew has always been assembled in a hurry, after a mutiny, from people who are mad enough to follow CaptainJackSparrow. You know what they say about beggar's choices.
According to Jack's Uncle, it's considered dangerous to go out to sea during a Blood Moon. Why, exactly? Because, back before Barbossa stole the ruby, the island that lead to Poseidon's Trident would open up a rift in the ocean. That would be pretty risky to sail so close to something you could fall in. Even years after Barbossa stole the ruby, it's a legend that's probably stuck until it turned into superstition of bad omens.
Why is witchcraft still punishable by death, when in the Real Life, it was no longer in force at the time? Well, it's been proven so many times that magic, especially voodoo and the like, is a VERY real thing. It wouldn't be unreasonable to think that witch hysteria still existed because reports of all the supernatural happenings in the series were filtered back to the public (perhaps even exaggerated a bit), thus sparking the continued hysteria.
Barbossa is able to use Jack's compass to lead Salazar there because Carina is on the ship with Jack. He's following what he really wants without even realizing it.
Captain Salazar and his crew were trapped in the Devil's Triangle and became vengeful ghosts after they died... because at that time, Davy Jones wasn't doing his job and ferrying souls who died at sea into the afterlife, so of course they had no way to escape.
Why would Jack be so vehemently opposed to the guillotine, as opposed to more barbaric and painful methods of execution? Because the guillotine is a quick, efficient execution. Whenever Jack has avoided death before, he's always had some combination of luck, charm, and friends/enemies planning to rescue him. He's even escaped being dropped from the gallows. Either way, he always needs time. A quick beheading cuts his options rather short, so to speak.
Young Jack Sparrow managing to defeat Salazar sets up the stage for the Brethren Court perfectly. With the greatest pirate hunter in the world dead and most (formerly) active pirates now dead save one ship, the seas and oceans of the world are unprotected and just ripe for the taking. However, learning from their mistakes the new generation of pirates know that a ragtag last-minute alliance wont save them from large-scale threats, so the pirate captains with the most power and influence come together and establish the Brethren Court with themselves as the Pirate Lords, the Pirate Code, the (hypothetical) position of Pirate King for times of crisis, and bind Calypso for an extra advantage/ace in the hole. It also explains what they would make someone like Jack Sparrow one of the Pirate Lords, because why wouldn't they want the allegiance of the man who outsmarted the dreaded Captain Salazar?
The dialogue and accompanying reference material of At World's End implies that the current Pirate Lords are not the first and that the Brethren of the Coast was established quite some time ago. It is more likely that Salazar's large-scale extermination of pirates forced the Brethren Court to convene as it seems to do in times of crisis. Salazar did mention that the pirates banded together in a last-ditch effort attempt to defeat him. This was likely the efforts of the Brethren to save themselves. Jack's defeat of this great threat to piracy would have likely contributed to him becoming a Pirate Lord.
Barbossa looks absolutely terrified when meeting Captain Salazar. This is for two reasons:
He knows of Salazar as the dreaded Matador del Mar, the killer of pirates.
He was previously a cursed undead pirate, long before Henry or Carina's time, from terrorizing people he's now being terrorized. A curious instance of Laser-Guided Karma here.
Will Turner warns his son to stay away from Jack - but Jack had saved his life. Well, Will has never really cared for Jack, knowing full well how unpredictable he is, so he may be giving fatherly advice to keep away from Jack. Also at this point he may be suffering A Fate Worse Than Death by being Captain of the Flying Dutchman and may justifiably blame Jack for putting him in that ship, even if it was only to save his life.
Another possibility is that Will is VERY aware that a man like Jack Sparrow has a sizable blast radius. Lots of old enemies, debts unpaid, and so on. After all, every single situation Will ended up in was directly connected to Jack in some way (Barbossa and the Pearl were Jack's, Davey Jones had made a deal with Jack, etc). It may well be the fact that Will is very much warning his son that being associated with Captain Jack Sparrow is all but inviting trouble
Jack seemed afraid of the idea of Will and Elizabeth having a child. This seems odd, as one might think he'd be happy for his old friends. Then you remember Jack and Will had Chronic Backstabbing Disorder with each other, and Elizabeth practically fed him to the Kraken. He's terrified of how much like his parents Henry is.
If one subscribes to the belief that the Dutchman's ten-year rule means that the captain must remain in "Davy Jone's Locker" to ferry the souls of the dead, then when Henry met his father at the beginning, Will might have violated this rule, and began succumbing as a result. Henry might have unintentionally worsened his father's predicament.
Destroying the Trident of Poseidon broke all the curses in the ocean, not just the Flying Dutchman's. However, not all the subjects of said curses were necessarily good guys like Will Turner. In what could potentially be one of the biggest cases of Nice Job Breaking It, Hero in film history, Henry and Carina may have busted open every damn can in the Seven Seas. Starting with the return of Davy Jones, if the post-credits scene is any indication...
