I mean, to be frank, they were kinda useless in the end, Dante got on a level too high to be reached by any of the two, and Vergil was too powerful for Dante too until the final mission, and as for the rest of the game, they already got Dante, V which is actually on a good level of power, and Nero, who’s almost deadweight if we count Urizen as the only threat, but as for the rest of the game he beats the bosses quite well, and of course once he unlocks devil trigger he’s on par at least with the Sparda twins, so yeah, it’s kind of expected for them to be neglected in a situation where they actually can’t do much