For example, I think it contradicts the narrative implied by many complaints about the rules around accredited investors and eligible contract participants and such that "the rich" benefit from important investment opportunities that are denied to less wealthy. It makes a case that joe-everyman can toss money into an index fund and out perform the wealthy.

I wouldn't expect 'given' year effects to be relevant, as it's averaging over a large number of people. Taxable is a better argument, since as you reach the highest marginal tax rates there is a lot of reasons to find ways to indefinitely defer paying taxes (e.g. die with it and pass it with stepped up cost basis).