2 shows that there are parasites that can control choppers and tanks, so possibly might not be the best choice. And keep in mind that Lady can cut through hordes of demons because not only is she experienced, her arsenal is loaded (Kalina Ann being the primary weapon) and most likely modified from the standard firearms.
The release trailer and prologue of 5 further shows that the military is woefully unprepared for a demon invasion.
In the form of a What the Hell, Hero? for Sparda, several fans have wondered why exactly Sparda didn't leave his family with the Vie de Marli for safekeeping considering that he helped them kill an evil demon god (which means that they probably owed him a favor) and that they were more than capable of warding off some measly demons sent by Mundus. The potential problem is never addressed in-game.
Considering Sparda's age, it's quite possible that he helped the Vie de Marli decades before meeting Eva. We also don't know what happened to Sparda, so maybe he planned to do it but was killed before he could.
The Vie de Marli could fend off common mooks, but what if more powerful demons were sent, or worse Mundus himself paid them a visit, like in the reboot?
The names of Sparda's keepsakes to Dante and Vergil, Rebellion and Yamato. Sparda rebelled against Mundus and sided with the humans, and Dante carries this with him as he rejects his demonic heritage. Vergil, on the other hand, is precise and quick with his sword swipes, even killing stronger demons with little effort.
There are subtle details that make a bit of sense regarding Eva's gold and red colors:
As implied in the first game, she's the one who brought not just Trish, but Dante back to life. Eva's hair is gold, and gold being associated with the ability to revive someone also applies to the in-game Gold Orb consumables.
Dante picking up his Heads or Tails? quirk in 2 may seem strange, using his coin several times throughout the game, before it's revealed that it's a trick coin where both sides are heads. However, in a bit of a Call-Forward, Dante in the first episode of TAS promptly picked heads when Morrison challenged him to a coin toss on whether or not to take the job of being Patty's bodyguard. He lost the bet with Morrison (it was tails), and it's been stated that he's never been that lucky when it comes to gambling, hence the quirk seen in 2.
A bit of a meta-example, and may also be a bit of a stretch, as it was one of the things responsible for 2's much weaker reception. Why is DMC2 easier than 1 and 3? Because it's the latest among the three within the series' updated Anachronic Order (When DMC5 was released, the official chronology became 3 > 1 > TAS > 2 > 4 > 5), and Dante has taken several levels in badass by then, making the enemies in 2 weaker in comparison. The game's easier because Dante is just that powerful now.
That also explains Dante's Awakening and its Nintendo Hard difficulty (at least its original release); since it was Dante's first major adventure.
With all those actions Dante got and Sparda being left in the backstory, it seems that another game that stars Sparda would be fitting. However, you don't need Sparda as a main character. You're already retelling his tale through his legacy, especially if you use his costume.
In the form of an Author's Saving Throw. There has been some speculation by fans as to why Dante is more sober and serious in 2, with one popular theory is that Trish and Lady (though the latter was not conceived yet) were killed or faced some other unfortunate fate and that he blames himself for that tragedy. Actually, if one recalls the events of the 2 prequel novel, he did experience a depressing loss in that he killed a Trish from an parallel universe who served and remained loyal to Mundus despite his efforts to convince her to change sides. It was stated the novel that Dante lamented having to go through with it.
With the release of new supplemental material and Word of God in the lead up to 5, Dante's demeanor in the anime (TAS) and 2 makes even more sense. The new timeline order is 3 > 1 > TAS > 2 > 4 > 5. Now what happened in 1 that could've made Dante so depressive? He had just encountered his brother for the first time in a decade only to find him brainwashed by the demon who had their mother killed and was forced to put him down. Note that he seems to return to his 3-style persona in 4 after meeting Nero — it's because he realizes he still has family that he starts to cheer up.
This also re-contextualizes the entire tutorial battle in 4. Here's Dante jumping in and "killing" the head of a clergy, eerie and antagonistic without even so much as uttering a word, when some young upstart with anger problems gears up to start fighting him without even remotely having a beat on Dante. Then the Red Right Hand of the Devil Bringer comes out, and Dante finally starts talking - that was the realization point for Dante, who goes from apathetically humoring Nero to indulging in a bit more of his flashiness shortly thereafter. The fact that Nero's own habit for showboating plays off of him only accentuates this.
At first glance Vergil, who is established as being an honorable Anti-Villain, stabbing Dante through his chest would seem as utterly lazy if not terrible writing in seeming to inexplicably turn Vergil into something of a Card-Carrying Villain out of nowhere. But when one considers that Vergil and Dante are well aware of their partly Demonic heritage, of which includes the benefit of Healing Factor, it would be obvious that Vergil would know that he wouldn't be able to kill Dante that easily and pierced him just to keep him down so he could leave with Dante's half of the Perfect Amulet and likely wanted to force Dante to awaken his Devil Trigger powers to help him survivein the new worldhe wishes to establish (via recreating the Kingdom of Sparda).
The games have generally established the idea that using a Devil Arm requires the user to be able to dominate the demon in some form:
Alastor and Ifrit in 1 attacked and possibly tried possessing Dante when he came across their Devil Arm forms.
The bosses in 3 seem to admit their loss to Dante, and offer their power to him. The one exception is Beowolf, whose soul/power is converted into melee armor by Vergil after failing to kill him.
Nero continues this trend in 4 despite not being able to convert demons into Devil Arms. Most of his abilities for the Devil Bringer are gained by absorbing the remnants of defeated bosses, or the alchemically-powered relics he comes across. This difference between what Nero can do, and what Dante has been shown to do, could be explained by the gap between their power and experience.
Vergil never lost Beowulf to Dante. Unlike every other Devil Arm in 3, Dante doesn't get a cutscene for acquiring it. And unlike Force Edge when using the Corrupted Vergil costume's Devil Trigger form of Nelo Angelo, he can still use it. Finally, a file in the first game says that Nelo Angelo can generate light when charging his attacks.
The reason for Dante and Vergil's Devil Triggers changing appearances depending on the Devil Arms equipped in both 1 and 3, as well Nero's incomplete DT in 4, could be attributed to them still being young and not quite fully grasping their powers yet. As The4thSnake points out in his video, the change in forms could point at the progression of Dante's power, where Dante finally settles in to his demon powers after defeating Mundus in 1 and thus his DT doesn't change in 2, 4, and 5. It's not until he overcomes his final mental hurdle in 5 that he unlocks his Sin DT. Vergil's DT changes between equipping Yamato and Beowulf in 3 and 4SE, but with Force Edge being the sealed form of Demon Sword Sparda, his DT is the default one. Nero's right arm in 4 could be explained that it was "locked" into Trigger due to the injury prior to the game alongside his desire to protect Kyrie. Yamato's acquisition awakens his demon power and influences his DT to being a manifestation of his soul/power because of the physical DT "lock" of his right arm. It's not until 5 where Nero fully grows into his own demon power, first seen through regrowing his right arm after Vergil ripped it off, and doesn't have to rely on any external influence to completely enter or exit his real Trigger, in large part due to his newfound storge love towards Dante and Vergil and past storge love towards Credo and Kyrie.
The series' Central Theme about how one's humanity is a source of strength and not weakness is displayed in Lucia's battles with Arius in 2. When Lucia first fights Arius, she has recently learned that she is one of his artificially-created demons and is terrified that she will become a threat to the people she's supposed to be protecting. When Arius defeats her, she even tries to goad him into killing her. When Lucia fights Arius a second time, she has reconciled with her origins while Arius has returned as a crazed demon. Lucia is at her strongest when she views herself as a person instead of a puppet Arius created, whereas Arius sacrifices his intelligence and versatile magic for demonic power he has no control over and thus, is defeated.
Arius is able to tell Lucia apart from the other Secretary demons despite her looking exactly like them. This ironically shows that Lucia is more human than she thinks as even Arius can tell the difference between her and the other artificially created demons who look like her.
As Nelo Angelo, Vergil's appearance resembles Sparda's demon form. This is a symbolism of how Vergil tried to emulate his father but failed, becoming a mindless slave instead of a feared and respected demon. Given it was Mundus who turned him into Nelo Angelo, it makes sense he'd subject Vergil to such a cruel punishment.
It's heavily implied that Dante's supernatural troubles prevented him from living a normal life. But when you think about it, how many times did Dante have to cope with the idea of an entire town being turned on its head because of a demon wanting to kill him?
TAS showed a bit of this, where demons destroyed a town Dante (calling himself Tony Redgrave), along with Ernest and his mother stayed in, being the only survivors. Ernest accidentally summoned a demon, and Dante ended up killing it, but this caused Ernest to view him as a monster, threatening to kill Dante should he come back. Just think, how many times did Dante inadvertently put people in danger because of something beyond his control?
Its also why Dante tries to keep his interactions with normal humans minimal outside of demonic jobs, Patty, Lady and Morrison. Its a cruel irony that Dante values his humanity more than Spardas power, yet its that very same race that rejects him for something thats not even his fault.