Hmm. That would explain why we've never seen him use any ability before and rely on swords instead, though the latter is also easily explained with Stain inspiring him. It would be interesting if that were the case, since that would mean it's possible to get the physical mutation only but none of the other things that ought to come with it. It would be as if Tsuyu gained the frog-like physiology, but isn't able to stretch her tongue, create acid, etc. All she'd have would be the exterior qualities, such as her eyes, lips, and hands.
I can't place a guess between being quirkless or not but I'd be interested either ways.
I wouldn't want the former to happen because I prefer this smaller, focused group for the League. That, as well as the fact that it would be boring if the only lasting antagonists are all from the same group. As you said, having a rogues gallery would be better.
That's... possible, but I think the figure looks different enough from Deku to not be her placing his image onto a past crush. Given Toga's ability to transform into people, I doubt she's likely to forget certain characteristics or features of a person either.