This analysis doesn't seem to account for the investments in and opportunity costs of, YC failures. Example: a company that takes $10m over three rounds and then dies.
Also, it seems to assume that without YC investment none of these companies would have been founded, and that no other investors contributed. They seem to be giving YC credit for the entire valuation even though they invested a tiny fraction of funding.
Finally, they seem to be double counting: estimating market valuation and then adding the effects on the economy. Those amounts are not exclusive.
YC would not put the $10M in, so from their point of view it doesn't matter. From the economic point of view it is simply statistics, a large majority of start-ups fails, the few that make it to round 'C' and then burn are not very significant. The majority will fail long before that or will survive.
Also, it seems to assume that without YC investment none of these companies would have been founded, and that no other investors contributed. They seem to be giving YC credit for the entire valuation even though they invested a tiny fraction of funding.
Finally, they seem to be double counting: estimating market valuation and then adding the effects on the economy. Those amounts are not exclusive.