I would think it isn’t very high—definitely not equal to population of 50%. And I can only think of a few woman (ruhl, Vogel and nottage) that have a body of work to select from for a season. I’ve linked 15 in this article and most I have not seen a play written by them.
I’m skeptical and wonder if something else is going on here besides Harris withdrawing his play—which I would think is a breach of contract at this point.