Funny how you bring up fighting games considering most fighting games poster-boy (Ryu, Scorpion, Jago, Jin, ect) tend to be pretty beginner-friendly but hard to master. Dante shoud be in the camp of "easy to use but hard master". The "gun stinger" example you use isn't really a better argument considering X+□+foward could be used as its stand in hell all gunslinger based weapon attacks could be mapped to X+□ depending what firearm you had equipped. Swordmaster Moves like shock for gigalmesh could easily be mapped to ○+/\ depending on what devil arm you had equipped.That is no different than a character in a fighting game where they have set moves locked behind certain stances and modes. It is a video game it shouldn't how much sense it makes although really it can based on how you look at it. Like why cant Dante use kick moves while in Balrog's Punch/Blow Mode and
Besides we already got a DMC game where Gunslinger, Trickster, and SwordMaster tech were locked into a single playstyle.
If Itsuno thought it was possible to regulate all of Dante's 4 fighting styles into 1 cohesive style he would just build off what 2 did and not separate them into 4 styles with DMC3.
I find it funny how people love DMC3 where your moveset are regulated behind styles and you cant switch between them at will and no problem DMC4 gives you that option now its a big deal. Also people's own point of reference of how flawed the Style system is the fact it was poorly implemented in a game that was rushed and incomplete. Why not wait and see how the Style System would work in a game that is actually designed and finished as the developers intended.
The Style System gives the devs more freedom to incorporate more moves and tech into Dante's moveset that wouldn't be possible without it. Not only that trying to cram all of his moves into some 1 style system will result in clunky moves and inputs that would greatly disrupt gameplay. Like for example trying to map Gun Stinger and Backslide into Lock-On + Shoot + Direction results into removing the option to walk and shoot while locked-on (a common tactic used by a lot of players) and would result into in a lot of unintentional Gun Stingers or BackSlides. Various SwordMaster moves like Prop and Shredder wont work in one button input. Pressing and Jump and Shoot at the same time is also very cumbersome (I mean DmC gave you the option to map those as its own button and I found that far more comfortable) in a fast action game otherwise other characters in DMC series would actually have such a combine input nor is something as amazing like TwoSome Time possible on it.
Also using other characters in the series in the series as an indicator is a bad example as an argument of removing the Style System none of those characters has the sheer volume of moves and variety in mechanics as Dante does as well as fill completely different purposes of gameplay compared to Dante.
You gain more from expanding the Style System then trying to streamline it into some uniform system. There are plenty of ways to make the Style System more accessible (that they are doing with DMC5 and it shows that Dante's gameplay is more positively received with game journalists than Nero's).
People loved 3 styled system cause it encouraged different play styles while also adding to replay as you upgraded styled through using them plus you only had 1 to focus on unlike 4 where you're bogged down with 5. Trickster movement could be mapped to L1 with L3+R3 could be used as devil trigger.