In the YC case, as a relatively small (very) early stage investor... they might very well benefit from a lot of very quick exits. Before additional investor dollars and the resulting dilution that accompanies it. It's plausible that this deal with Facebook is designed to achieve that. Essentially giving Facebook early insight into these companies and that ability to pick them up for cheap ($2M-$10M), which might actually be advantageous for YC.
I'm not saying that's what is happening here. I really have no idea. I'm merely point out that Calcanais might have a strong point.
they might very well benefit from a lot of very quick exits
I fail to see how. Before they closed their Sequoia round, you could argue that smaller exits help YC keep afloat. With millions in the bank from outside funding, YC is beyond the point of trying to keep itself afloat.