Eh, I think I have a better answer...
Because weak characters are usually boring and typically drag any sort of media down regardless of their gender.
In other words, he has a good reason to make a female character good... it (usually) makes the overall story better!
Yeah, seriously. That answer he gave was terrible. The implication is that if sexism went away he'd no longer be interested in writing interesting women...
Which I think couldn't be further from his actual intentions. Sometimes people get so fixated on making their enemy look bad that they lose sight of the stuff that's actually important to them. And a lot of these people end up being called SJWs (or MRAs or bigots or what have you on the other side)
I for one appreciate his stories and characters, I think he generally does a good job with them, both male and female. I'm personally tired of seeing so many movies where women only serve as the love interest/goal (yes, that means I agree with Anita Sarkeesian on something) and I like a lot of movies where this isn't the case, especially if they're not also hamfisted about social issues. But I think we got this way because people - everyone, men and women - generally feel safer with and more compelled towards exceptional men than exceptional women. Where "exceptional" means people who are both unusually good or interesting as well as people who are unusually bad or dull. I could get into a long explanation as to why I think gender dynamics ended up that way but I don't really want to subject people to that unless they want it >_>