The rate of return (%) has been better for pension funds, IRA, 401ks invested in market wide index funds than the wealthy that have invested in active hedge funds. (This has been very true historically, especially net of fees.)
So it's fair to say that the wealthy have seen worse returns compared to the public. And that the public has seen the "lion share" of market growth.
Still, I highly doubt that the asset allocation of the median investor of the bottom 90% is similar to that of the median investor of the top 10% -- even if PFs have access to the same vehicles that HNW/FO have.
Wealth is definitely skewed. But, if you're willing to accept the wealthy have allocated more to HFs which have underperformed market, recently, it seems that the "common man" have outperformed by keeping it simple and letting their automatic biweekly 401k contributions go to VOO instead of some highly complex financial product.
EDIT: simplified wording
I think it’s wrong to say these stock market gains have been enjoyed by “the people” when the richest 10% enjoyed the lion’s share of them.
1. https://en.m.wikipedia.org/wiki/Wealth_inequality_in_the_Uni...