Yeah, my supervisor for my undergrad thesis is a brilliant researcher who's still publishing good work 20+ years into his career. He was just a normal dude in undergrad who started in engineering but switched to math because he disliked project management, and he certainly wasn't in any sort of "young genius" program through grade school. But his PhD thesis was runner-up for best in the country, he consistently presents at all the major conferences in his field, and he has even won a few teaching awards.

But doesn't that just back up the thesis that the educational system is not helping them reach full potential?

Has nothing to do with meritocracy.

It's not about what those individuals deserve, it's about the societal return on the investment of their education. The potential return is simply greater.