I don't know if this has been mentioned but I can't easily distinguish in villains between the 1 star and the normal girls. This means I can't easily tell when I finish a villain tier and its time to move up to get the normal girl in the next tier. This is somewhat annoying.
Also, if these girls require any upgrading it's going to increase the problem I already have trying to max out all my harem girls.
I'd just as soon not bother with them.
Oh I thought of another disadvantage. I collect yman manually from harem girls. It is a pain to collect it from 350 plus girls, so much so that I'd like to be able to kick out girls with scant contributions. The last thing I want is more deadbeat girls to have to wade through. I don't want them.