Well, the title does also say overhaul as well as rewrite so who cares about plausibility, honestly.
Main point: Make Dante, Trish, and Lady less dumb to begin with and have the characters' campaigns as follows.
Lady: Her MO after 3 is "stopping demons like my father from ever coming about again", and demons like her father are humans who seek demonic power for selfish reasons, so she should be the first person firing a bullet in Sanctus's general direction but instead she was on some "dey took 'er jerbs!!!!" b.s. so give her a slightly-before-4 campaign where she investigates Fortuna and the Order and what they're about [she may or may not encounter a woman in the Order who's sussing her out] then reports to Dante with her findings to get him on board. She's also not voiced by Kate Higgins.
Dante Part 1: He not on board at first and he's cranky. He may or may not also be a drunk but it's presented 100% as the completely uncool trait that it is. Lady throws in his face that he's upset about Trish leaving... again. The first time was because she wanted to freelance and the second time she didn't bother telling him anything and he hasn't heard word of a blonde with lightning abilities around the world or anywhere. Whatever. Lady leaves, Dante goes about his business until his shop gets ransacked with him in it, Eva's portrait is broken and Dante's weapons stolen [Sparda, Pandora, Gilgamesh, Lucifer, etc]. He has a boss fight with the nameless assailant who shows off an Ascended form proving Lady's suspicions correct. Dante loses the fight because he's not in top shape. The nameless assailant marks Fortuna on a map and tosses Trish's bracer at Dante as a taunt. Dante gets his act together, shows up to Fortuna and shoots the Pope. Gets a boss fight with Human Form Credo.
Nero Part 1: When Dante shows up to shoot the Pope, Nero gets Kyrie to safety then goes back in to help Credo out, cue Nero vs Dante fight to give a diff POV on what it's like to fight against Dante rather than as him. The assailant from point 2 shows up for the assist, who is Gloria for people that don't like putting 2 and 2 together. Dante leaves. Nero's ordered to investigate Dante's presence in Fortuna so cue his campaign happening close-to-as-is except instead of b.s. "he beats the bosses once and they escape so that Dante can Kill Them For Real but still not get them as Devil Arms", he absorbs them wholly into the DB and gets the Chaos Legion gimmick of summoning them and/or using their related powers to traverse the map and kill enemies or imbue his DB with their element. He awakens Yamato, all that other junk. Nero fights Angelo Credo after Credo is tricked into fighting him, but Kyrie is there. Instead of her getting kidnapped in the most useless scene to ever have a kidnapping, Agnus frames what's going on with Credo and Nero as a matter of emotional compromise and weak will (a.k.a. neither Nero nor Credo have what it takes to actually save Fortuna), so Kyrie takes it upon herself to make up for their failures by assisting Sanctus in a demon-free utopia where her brother and boyfriend cannot. She's obviously not told about being a battery to the Savior but whatever. Nero pursues Kyrie and Agnus across the rest of the map, fights Dante the second time and everything, but when Gloria shows up, Gloria doesn't apprehend Dante even though she was ordered to. She instead knocks Nero out and gives him over to Sanctus to use as a battery for the Savior.
Gloria: She gains a separate campaign from there to reveal that she used to be Trish but abandoned that identity. Not only was she tired of being a lightning-powered Eva clone, Mundus wouldn't allow his creations to live independently from him in case they betrayed him so he created her with a self-destruct failsafe. She at least had some consideration to not die anywhere near Dante so she left the office for a "final" time and traveled elsewhere. Wound up in Dumary where they (probably Matier) extracted Mundus's failsafe and contained it in the Evil Heart, and gave Trish the Healing Heart to recover from the damage it caused. She adopted the name Gloria and changed her look and fighting style to distance herself further from Mundus [and Dante by extension]. Whispers in Dumary about Fortuna's shady actions prompted Gloria to investigate but she was caught by Agnus and experimented on to give her the Angela Gloria form, forgetting her former life as Trish and allegiance to Dumary as a byproduct. She's all better now thanks to a boss fight with Dante to knock her back into her senses before they encountered Nero that second time. Anyway she knocks Nero out and hands him to Sanctus to use as a battery, but Dante isn't there and Sanctus doesn't have the Yamato in his possession. Gloria passes it off as Dante having stolen it from Nero sometime before she encountered him, and she had to apprehend Nero before he complicated Sanctus's plans since Credo didn't do it. Sanctus accepts that reasoning because he didn't read the script ahead of time or google search "Who is Gloria" before the scene even happens.
Dante Part 2: Starts with a boss fight against Angelo Credo because Credo is 10000% aggravated that he's about to lose both his sister and brother-in-law to a despotic old man being helped by people who should know better. Dante defeats Credo to make sure he doesn't go on a suicidal mission to stop Sanctus. Gloria and Credo help evacuate the people and destroy demons and Bianco Angelo armors where needed. The rest of the campaign to destroy the Hellgates happens as-is except Dante doesn't have to re-fight any of Nero's bosses, and he gets his weapons back. And everyone rejoiced, because re-fighting the same exact bosses in the same exact environments is a waste of everyone's time. Dante also has the Yamato, because letting Nero remove it from Agnus's lab in the vanilla story only for Sanctus to get it and give it back to Agnus was also a waste of everyone's time. I mean, they really could have shortened that to Nero getting his DT and Agnus managing to sucker punch him and steal the Yamato anyway for the rest of the plan to go through, but I guess this is why I'm not working for Capcom. Anyway while Dante is doing this, the Savior is drawing energy from the bosses Nero absorbed into his DB. That's not as bad as a scenario where Dante was used as the battery, because Nero's unique ability to absorb other devils serves to have their power act as a buffer to his life force. The Savior has to drain three devil bosses worth of energy before it gets to Nero directly and draws from his strength. Dante totally knew all of this, because being more intelligent than he lets on is Absolutely A Thing. The campaign closes out with Dante fighting the Savior [directly controlled by Kyrie inside the Mind Core, cue highly telegraphed attacks], where Dante gives Nero the Yamato so that he can wake up and get Kyrie out of there.
Nero Part 2: Remove the dice game. Nero fights through newer versions of Berial/Echidna/Bael+Dagon that function as hybrids/fusions of each other since their energy was being mixed into the Savior and becoming less distinct. Nero re-absorbs them into his DB and gets even more skills. The rest of the campaign continues as-is, with Nero rescuing Kyrie.
Vergil: Has a gravestone with his name on it that can be spotted in the background of a random mission or other. His inclusion in the series was a mistake.
