I think this is simply false as a matter of fact. See this comment.

Ah, I was speaking in terms of finding talented researchers at the graduate and faculty level, not lvy league undergrad admissions. Your comments seem reasonable on the subject of undergrad admissions, which I agree are almost wholly negative selection filters. Do you think this also goes for graduate admissions? What should we anticipate observing if schools were bad at this kind of selection? What would we see if they were good at it?

EDIT: I'm working largely on the observation that getting a PhD in any field is really very easy. The major barrier seems to be interest. This doesn't go for all fields, of course. Law is a serious exception. But physics? Mathematics? I lack data here, but I'm skeptical that these are particularly closed academic fields.