Classic Darkwing had always implied that Drake's obsession with fame and glory could have turned him evil, or at least with disregard for collateral damage, if Gosalyn and Launchpad hadn't stumbled into his life during the pilot. When DuckTales started up and Darkwing was a TV show... Jim Starling was missing two people: Gosalyn and Launchpad. Without their ability to rein him in and focus on the bigger picture, Jim Starling slowly turns into his worst self, Negaduck.
Even moreso, the original series episode "Time and Punishment" reveals that this would have been one of DW's possible futures: if Gosalyn had disappeared while he was on the job, his lack of a restraint on how much he could do for heroics would make him into Darkwarrior Duck.
It's also worth noting that the show-within-a-show version of Darkwing may have also been darker because he lacked those elements, which would in-turn explain the deconstructionist direction the movie would have taken. Examining what separates a hero from the villains he fights when his methods are just as brutal isn't a good adaptation of Darkwing Duck, but it was arguable a part of the point of Darkwarrior Duck.
The first scene in the episode is a clip from the in-universe Darkwing show, where Darkwing says his Let's Get Dangerous! catchphrase as he goes up against the villain... and then does not gain any competence; instead he immediately proceeds to step on three landmines, getting Amusing Injuries and accidentally subduing the villain by falling on top of him. Severe misuse of the catchphrase... or a subtle hint that Jim Starling isn't the show's "real" Darkwing? (Juxtaposed with the cliffhanger where the villain turns out to have Darkwing's face.)
Plus, if you listen closely to the masked crook's voice at the beginning, he sounds like Negaduck.
Given that Darkwing Duck seems to be exclusively known as a TV series in-universe, why wouldn't they contact the actor to at least make public appearances? Consider all the footage of the in-universe version we've seen. It's super campy and silly, and while Launchpad may take it seriously, no one else seems to. That's the reason; the TV show is the equivalent of Batman (1966), and the director is specifically trying to distance the new, gritty portrayal from the comedic original. The last thing they want is to remind people how silly it used to be.
Similarly, the enforced Locked Out of the Loop was something that happened to Clayton Moore, the 1950s' Lone Ranger, when the (relatively) gritty reboot The Legend of the Lone Ranger was being produced in 1980. Up to and including forbidding Moore to make any public appearances as The Lone Ranger and even banning him from wearing his iconic mask. Fortunately, the idiot executives belatedly came to their senses and relented on the whole mask thing.
And the glasses Jim Starling wears at the furniture store opening are remarkably similar to the ones Clayton Moore wore during the "mask embargo" while making public appearances as himself.
The fact that Darkwing's new performer is a fan of the old show also reflects how many of those involved with Batman's later series and movies, including actors, writers and directors, have admitted their fondness for Adam West's show, being the way many of them became fans of the character.
Almost all of the in-universe Darkwing Duck footage we've seen shows the character fighting one or more of the Fearsome Five — except that, every time, Negaduck has been conspicuously absent. It was all Foreshadowing for the reveal that Negaduck wasn't a villain on the show — he's real.
Just like the Fearsome Five in the original series, Jim's Start of Darkness as Negaduck is similar: A once renowned person whose life was hit hard by an encounter with DW. The pattern is all played out:
Bushroot: A botanist whose otherwise idiotic colleagues laughed him out of the lab, forcing him to experiment on himself and become a plant-duck hybrid, with DW stopping him from completing his revenge.
Liquidator: A crooked water salesman who was initially stopped by DW, but became a dangerous force to be reckoned with when he merged with the chemicals he was using to contaminate this rivals' water supplies.
Quackerjack: Mad toymaker; despite lacking a proper origin story, it was said that he owned a toy company, and once he went bankrupt, he blamed video games for 'corrupting' children so they no longer appreciated his toys, not realizing that much of his misfortune came from making downright dangerous toys; again, DW stopped him from achieving revenge.
Megavolt: DW's old schoolmate, tried to rig a homecoming dance but was stopped by DW.
2017 Negaduck: An actor who once played DW, but was driven insane by a fantasy of reliving his glory days, becoming the Evil Counterpart to the new Darkwing Duck.
In a way, this makes him very similar to Quackerjack; both of them lacked an official origin story in Darkwing's show, are Badass Normal instead of gaining superpowers like the other Fearsome Five; and they went crazy out of a perceived lack of respect for their work, not recognizing their own mistakes, and putting all the blame on their replacement (video games for Quackerjack, a new Darkwing performer for Jim).
He also embodies the darker aspects of the original Darkwing's personality is also likely a nod to "Negaduck I" from the episode Negaduck, where Negaduck was quite literally Darkwing's dark side given form.
Similarly, new actor and now In-Universe real-life Darkwing Drake Mallard embodies the redeeming qualities of the classic Darkwing, including his drive to do good.
Just like Launchpad can survive pretty much any crash with little to no damage, Drake can resist insane amounts of punishment. While this is a reference to Darkwing's show relying heavily on Toon Physics, it also shows how much being Darkwing's fans influenced them both; they admired the character so much that they trained their bodies and minds to resist injuries that would incapacitate or kill anyone else.
It could also be a reference to how Jim Starling did all of his own stunts for the original show; they admired him so much that they both trained enough to do the same!
Scrooge is shown to be enormously out of his depth in making movies, claiming he hasn't seen one since the late 1930s. He also showed little interest or desire to go for a big blockbuster movie, preferring to keep his studio focused on simple and cheap workplace safety videos. This all makes sense from a financial standpoint as blockbuster type movies can be prone to severeCritical Dissonance and enormous subjective appeal to audiences. There's no guarantee that the money put in would be made back and the chance of success is down to a lot of luck, something Scrooge shows some rather large disdain for.
Scrooge notably keeps his own personal demands for the film minimal and simplistic. He outright admits this is an area he doesn't have a lot of experience in so he's deferring to someone that does have the expertise he lacks. His low level requests likely come from the fact that he recognizes how much damage could happen if he gets too involved while knowing pretty much nothing.
Putting Dewey in charge is justified by the fact that children would be the target audience so he's the best voice to listen to. But bear in mind that Dewey has seen the show the movie is based on and is also close friends with Launchpad who's a dedicated fan. Either Dewey knows enough to make the movie more approachable to audiences or Launchpad can offer input and be heard because of his friendship with Dewey.
If one pays close attention to the two Darkwing costumes, Drake's Darkwing costume closely resembles a modern superhero's spandex costume versus Jim Starling's OG Darkwing costume (that more closely resembles a pulp action hero's Civvie Spandex outfit). This can be seen as indicative of how in real life spandex-wearing superheroes like Batman took the place of the older pulp fiction heroes like The Shadow.
It's also a more practical take on the original costume, which is also a modern superhero film convention. The original Darkwing Duck wore a coat with his cape attached around his collar. Drake's costume is a vest worn over a long-sleeved shirt, with the cape running over his shoulders and attaching to his vest buttons. The new costume appears to be designed to capture the look of the original, but offer a better range of motion and a cape that detaches more easily.
Jim Starling's name has been a subtle hint to his true nature. It's a bird pun (naturally), but it also brings to mind Jim Starlin, creator of one of the most dangerous villains in the Marvel Universe, a fellow you may have heard of called Thanos.
Bird puns aside, given they all share a first name, it could be a dual reference: both to Starlin and Jim Cummings, Starling's/OG Darkwing's voice actor.
He also believes that he’s a great television star, but he's actually a lesser star - a star-ling, one could say.
Why does Jim Starling's predominantly purple costume become yellow and red after heavy exposure to water? The costume was likely dyed to save on budget, and the jacket became that shade of yellow due to decades of disuse.
It also could be that the costume was meant to be worn by either Jim himself or another actor playing what was more or less the show's version of Negaduck. Going with this, Jim would have already been informed while shooting about the character and so either receive a new suit to wear for the role or know one of his co-workers received it and be able to ask for it himself once the show's cancelled. In either case, when his show was canceled he hung onto it and at some point over the decades had it dyed.
Genius Bonus: Whether or not there was bleach in the water, there is the fact that any color of fabric will become either white or a yellowish color when exposed to it. In addition, if there was bleach in the water, it could have been used for a scene involving DW to swim through a body of water and it was added into the water in order to keep any bacteria or microbes from forming.
Launchpad saw through Jim's lie about the actor quitting due to stubbing his toe, because he saw him drop a working flatiron baseside down on his foot and managed to walk it off. Someone who can take that sort of pain wouldn't be stopped by a stubbed toe.
A minor thing: Johnny from Ottoman Empire, the host of a furniture-themed TV show, would have been a logical guest for the opening ceremony of a furniture store. Sadly, due to the behind-the-scenes drama between Johnny and Randy, only Jim Starling was available.
Why did Dewey dance the Perfect Cast? Because, as it was established a few episodes ago, he's a fan of Powerline and may have learned some of his dance moves.
Why was a swan, a bird associated with beauty and peace, the chosen species for the director of a grim and gritty Darkwing Duck reboot? In real life, swans are ferocious birds.
As an interesting background detail, the "gritty" movie villain Megavolt, though briefly seen, has a design suggesting that (within a world of Funny Animal rats and ducks) this is supposed to be a "realistic" take on a high-voltage, electrically-themed villain. This helps explain how, when Starling makes his move, it turns out that the prop used for his electro-gun can be used as a real weapon.
Alternatively, the working electro-gun prop might have been an addition of Dewey's rather than Boorswan's. Considering Dewey had already added stuff like chainsaw jugglers, it's not out of the question that he would ask for a cool-looking weapon without thinking of the consequences.
Fridge Horror
Imagine how horrifying the situation would be if Jim saw a finished film without Dewey and Launchpad ever getting involved and considering how Ax-Crazy Jim is...
Also imagine if the studio did tell him about the movie and tried to get him involved. Would Starling really settle for a Remake Cameo?
He'd still be trying to make trouble at a company owned by Scrooge McDuck. He'd only get so far before he was stopped. The real fridge-horror is that this means we never got to see Scrooge McDuck and Negaduck fight.
Fans took this as meaning there was a Gosalyn in the Show Within a Show, but she's never actually seen. As it would turn out Jim Starling was no Darkwing.