This game is a good prototype for how Dante could utilize a Devil Bringer mechanic.
I didn't feel that Nero was even necessary in DMC4, as Dante could easily have learned or acquired the Devil Bringer on his own somehow in the story, and it could be utilized in a way similar to this game.
How they would go about mixing a Devil Bringer with several style moves (buttons-wise)? I don't know, but at least this game shows there's some potential to expand on the original Dante's fighting style (even if this one didn't really succeed properly).
Well, they mainly introduced Nero to appeal to new players, but also because they claimed that if Dante had the DB he wouldn't play like Dante anymore.
Personally, I don't care for the DB mechanic. Although they should just come up w/ another gun/style combination to implement it (like Kalina Ann w/ Gunslinger, except faster & usable in mid-air) if they really insist upon it being in the game.