That's being pretty generous. If anything, I'd assume that a YC-backed company knows less about hiring than BigCo HR departments (assuming we're talking about software companies). Most BigCos got to where they are for a reason. A lot of YC-backed startups have never hired a single person before.

They know more about some things and less about others. They know less about employment law and benefits administration, but they are probably better at judging someone's programming ability.

Except that BigCo makes arbitrary hiring decisions without flexibility. Isn't part of the benefit of YC-backing to get advice from people on things such as hiring?

I'm not trying to put YC down. I'm just trying to add a dose of realism here. Yeah, these companies get advice from experienced people. That doesn't make them superhuman though. Everyone makes dumb mistakes when they're new, no matter how intelligent they are or how much good advice they get.