They don't receive "nearly all of the benefit", they are just doing a bit better than the market consistently. This feels like a motte-and-bailey argument, with the motte being the examples of Buffett etc. who in a certain sense seem to be beating the market, but not dramatically, and the bailey being the claim that one can win much more than the market by noticing opportunities early.

(I mentioned lottery as an illustration for the importance of being able to affect the outcome, that mere existence of people beating the market is insufficient. Whether it's possible to affect the outcome is a separate question that you are now addressing.)