For three games now both Nero and Vergil have been designed under the mindset of
Dante with less tools to do everything but easier due to having less moves, a stronger gun, snatch/trick to make staying on enemies/keeping them juggled very simple and flashy cutscene moves to do damage without a long combo but have judgement cut/exceed just frames to give you something to sweat with"
But Vergil has a lot more going on then Nero, yamato has about as many moves as red queen but then he has two other weapons. doppleganger and SDT give you all the perks of neros DT (afterimages, big iframes pop that launches enemies, big cutscene attacks) but bigger/better/more and stuff like bringer knuckle is just a more limited version of sword formations.
Besides wasting dev time appealing to fanboys/girls of both characters, what reason is there for a future DMC game to have both of them? is there a way they can flesh Nero out more that isn't just arbitrarily giving him stuff Dante used to be able to do like stop time or surf?