The author seems to conflate YC with all Silicon Valley startups. This is clearly not the case and I would argue that if you are looking for big, world-changing ideas and only considering YC companies, you're looking in the wrong place.
I mean, I bet James Gosling feels that Java is a disproportionately better programming language.
The last startup to have much impact was probably twitter, and there hasn't been much else before or since in recent years. Groupon is big now, but in a couple years it'll probably be sold for fractions of a cent on it's acquisition cost to someone who thinks the brand name and mostly defunct email list still have value.