He then becomes CEO of YC. But YC is already a well established and successful outfit at that point so there is hardly any risk involved. The chief requirement is just to not screw up a good thing. So far he has managed to do that.
Along the way he makes many more millions because as a YC insider he gets to invest at the earliest stage for the best looking start-ups.
I have nothing against the man and I do not begrudge him his millions but lets stop thinking he is a genius. He is an average entrepreneur that has had an amazing slice of luck by being in on YC at its start and making the most of it. I'm sure he is a smart, hard working and a nice bloke. But he is not a genius.