I think that's the risk-reward trade-off. At the most elite levels, it'll all be about survivor bias. So even if that technique only works some of the time, those that it works on will have a better chance of becoming elite.
>BS. If that was the case, then YC would be a non-profit and they would accept everyone.
I could see the argument for the first (non-profit) but not the second (accept everyone). Filtering down to a set of folks that they think they'd be able to most effectively help would make a lot of sense regardless of reason for doing.
There's probably some bias here where no parent is going to want to admit that they've treated their kids differently (likely unintentionally). Not to say that there isn't useful insight here anyway.