Nero would be a little upset about that
In a way it would make at lot of since and also portals being open don't happen often and im sure only weaker demons can sneak through never giving Dante or nero a taste of what powerful demons can dish out
Well, when talking about demonic portals, remember that the ones in DMC4 where Berial, Echidna and the others come out of are portals too. I'd say those demons are quite big