And that's why this move is a smart one : Yuri has effectively outsourced all the valuation work for the investments onto really smart people that he doesn't have to pay anything for.
While that doesn't seem particularly fair to the rest of the VC community, it's exactly analogous to investing in an S&P ETF (which just invests in a whole bunch of stocks at the current market prices).
YC now has more partners and a larger network of alumni so that should help a bit with scaling this.