Are you claiming that a mutual funds' performance evenly benefits anyone with a 401k?
In the last 40 years 0.00025% of Americans have tripled their share of the wealth. Of course everyone with a 401k has benefited but they are nowhere close to the main beneficiaries of capital gains.
No. The share of wealth of the top 0.00025% has tripled.
The pool of people people in that quantile is dynamic.
In 1980, that was about 600 people. In 1980 the richest person in the United States was J. Paul Getty. I imagine most of those people are no longer alive.
In 1980, Jeff Bezos was 15, Bill Gates was 24, Larry and Sergey were 6, and Sergey had been living in the United States for 1 year. It's likely that the effect you're seeing is an artifact of the role technology plays in the economy rather than exploitation or rent seeking.
In the last 40 years 0.00025% of Americans have tripled their share of the wealth. Of course everyone with a 401k has benefited but they are nowhere close to the main beneficiaries of capital gains.