That's rewriting history, including a lot of hard work by a lot of people. YC disrupted the model, it didn't start it. PG repeatedly describes YC as a startup in changing how this works, so mistaking their growth with the industry misses what's happening.
The dotcom era had incubators through models like "I have access to capital but no one good idea; let me start a bunch and pick which to go". VCs regularly host EIRs (entrepreneur-in-residence). More dominant, many universities, corporates, and in gov, SBIR. Not sure how the numbers of SBIR compare to YC, but given SBIR is based on a % of each US dept's budget... ;-)
The "startup accelerator" changed the model: more $ to more varied entrepreneurs, structured program with educational eco-system, made VC capital more attractive, etc.
