What "superinvestors" are you alluding to here? Are you suggesting that getting investment advice from Graham is sufficient to reproduce the kinds of returns he and Buffett have had? Because that seems like an unrealistic expectation, and a totally orthogonal argument to whether or not investors can "beat the market". It's like talking about Google and then asking how many other Stanford CS grads never went on to start successful tech companies.

Learning from somebody good doesn't automatically guarantee you'll end up being as good as them afterwards, for a variety of factors.