Sam's contention, as far as I can tell, is that YC is hugely important to economic growth. Startups are a small fraction of growth. Of that small fraction, a fraction (20%) require VC funds. Of that fraction, another fraction may not have made it but for YC. So, we're looking at a fraction of a fraction of a fraction that YC is involved with. I'd say that suggesting that YC is hugely, or even just important, to economic growth is absurd (and reflects the massively outsized view SV has of itself).