A pyramid scheme is a zero-sum game where wealth accrues up the pyramid in exchange for promises of future riches to the new recruits. YC startups thus far have

A pyramid scheme is a zero-sum game where wealth accrues up the pyramid in exchange for promises of future riches to the new recruits. YC startups thus far have been a positive sum game to the tune of $4 billion. Additionally, new YC companies aren't required to pay anyone for the things YC provides (as opposed to a pyramid scheme).