He shouldn't use that $22 million average value for these calculations. It's based on current values of often quite young startups, not exit values. As I say in the post, "unless the top VC funds as a whole lose money, this number should be a lower bound on actual exit valuations."

His math also assumes you invest randomly in YC startups. Any angel who was paying attention ought to be able to narrow the field a lot, which would justify proportionally higher valuations.