The problem isn't that big-breasted women exist in videogames, it's that they are a disproportionately large group compared to average-breasted women. And they often dress like whores for cheap sex appeal that doesn't really mean anything.
If it's parody, fine. If it's logical (for whatever reason), fine. If it's a plot point (Probably not, but I've seen weirder), fine. If your game is about sexual stimulation, fine. But making women look sexual for the simple sake of having sexual women? Or (what I assume the feminists consider) worse, don't even do it consciously? That's bad.