I would say that the operative questions is more about founders who become successful after they were not accepted into a YC "class." YC themselves are good at pointing out that most start-ups have to change direction/pivot multiple times before being successful. That's why it's about the people/founders imho.

I also suspect that there is little correlation in terms of success or not for companies accepted/not accepted into YC. The one exception worth exploring is that moving to SV for 90 days for non SV companies and working in one living room might increase focus and hence chances of success. That would be interesting to know.