(1) Conditional on having applied to YC, YC finds that having attended a prestigious college makes one no more likely to be selected for interviews.
(2) Conditional on having been selected for YC interviews, YC finds that having attended a prestigious college makes one no more likely to receive YC support.
(3) Conditional on receiving YC support, YC finds that having attended a prestigious college makes one no more likely to succeed in the market (here defined as visibly thriving within about a year).
Given the initial essay's strong emphasis on market success as the ultimate verifier (paragraphs 5-8), I thought the main idea was (3) -- but if interview invites/subjective-evaluations are a factor, some amount of (1) and (2) are mixed in, too.
That is a completely different statement than showing that it doesn't matter what school you went to. Your article appears to me like it is conflating the two.