I don't think he's necessarily bad for feminism, because he does write well rounded women/girl characters and often shows very graphically the way women in society are manipulated by the power structure even when extra-ordinarily gifted and Buffy, at least, was surrounded by foils (Willow with her much more serious attitude, Faith with her wild amorality, Cordelia with her superficial flighty high-school girl normality). However, he isn't the end-all be-all either. He has some very definite blind spots in the kinds of women he chooses to write and he seems to have some pretty bad madonna/whore issues. IMO, the problem, though, isn't really Joss writing superheroines. The problem is that there aren't enough regular women in surrounding media doing regular jobs. You can have a Duncan McCloud (Highlander) when you also have most of the cast of NYPD blue.