So arguably at least one of {pg, pb, etc.} could have made just as much value over the past ~10 years by starting another startup, instead of an YC, if that were the goal. 10 years is probably enough time to try/fail-fast at least 2 and maybe 4 times, each.
Probably, but you're only counting the tangible value. In my mind what they've done is far greater in intangible value. What about HN and the community it has nurtured? And let's not forget being a sort of pointer to true north to most of the people thinking of creating something out of nothing. Sure, money is easy to count and imagine, but there's plenty of people that make that, how many PG's appear every 10 years? To paraphrase Michael Scott - you think PG's grow on trees; well they don't; there is no PG tree.
Absolutely - I think YC's overall "consumer surplus" is over $10b, since it somewhat changed the game for early stage startups in general, not just startups in YC.