I'll give you this: "It's hard to argue I'm biased against female founders when I have a female cofounder myself" is a weak sentence. Yes, you having a female co-founder is strong evidence, but if you do sexist things then it doesn't make it any harder for me to argue you're sexist. The "it's hard to argue" part doesn't belong there, it belongs after he's not only explained who he chose to start YC with, but how YC and he have acted in relation to others in the industry, which stacks up extremely favorably.