The point is not that people are becoming rich by investing in index funds, but that rich people mostly do no better than people investing on those funds. Rich people are not special as a population, except for having a lot of money.

Except that this is a much more complex affirmation than it appears. I do think people making this point are deluded, ignoring the complexity of the situation. What, of course, does not mean that they are wrong, only that the affirmation doesn't add any new information,