If we're talking cannon, then, yeah, it's all absolute BS. Vergil having Dplgngr is just as bad as suddenly having Yamato open portals. It's not how that works and it's clear that they only added because it was in DmC. If the thing could open gates to hell, which is apparently the case since that's what happened in the prequel novel, then DMC3 would've been a very different situation, or, as I usually put it, why DMC3 at all? Gameplay wise we'll have to see but I honestly think the DmC moves are very unimpressive to look at, even when DMCVergil is pulling them off, which isn't usually the case. DmCVerg looks like someone copying moves. Just look at the way he does Upper Slash compaired to DMCVerg (2:00).
The issue, though, is that I saw how Vergil fought at the end of 5, during the credits, and his animations look much more like the ones in DmC. As it is the moves are not particularly interesting to look at so I'm not a fan, but when they look just as unimpressive in 5 as they do in DmC I kinda become disillusioned.