Your statement about no investors beating the market is demonstrably false. Look at Michael Burry for example. What the statements about index funds say about is the average investor, not the atypical high performer. The argument is also weakened by $0 commission trading which did not exist when those studies were being done.
https://en.m.wikipedia.org/wiki/Michael_Burry
> After shutting down his website in November 2000, Burry started the hedge fund Scion Capital, funded by an inheritance and loans from his family. He named it after Terry Brooks' The Scions of Shannara (1990), one of his favorite novels. He quickly earned extraordinary profits for his investors. According to author Michael Lewis, "in his first full year, 2001, the S&P 500 fell 11.88%. Scion was up 55%. Burry was able to achieve these returns by shorting overvalued tech stocks at the peak of the internet bubble.[13] The next year, the S&P 500 fell again, by 22.1%, and Scion was up again: 16%. The next year, 2003, the stock market finally turned around and rose 28.69%, but Burry beat it again, with returns of 50%. By the end of 2004, he was managing $600 million and turning money away."[6]
In 2005, Burry started to focus on the subprime market. Through his analysis of mortgage lending practices in 2003 and 2004, he correctly predicted that the real estate bubble would collapse as early as 2007. His research on the values of residential real estate convinced him that subprime mortgages, especially those with "teaser" rates, and the bonds based on these mortgages, would begin losing value when the original rates were replaced by much higher rates, often in as little as two years after initiation. This conclusion led him to short the market by persuading Goldman Sachs and other investment firms to sell him credit default swaps against subprime deals he saw as vulnerable.[14][15][16]
During his payments toward the credit default swaps, Burry suffered an investor revolt, where some investors in his fund worried his predictions were inaccurate and demanded to withdraw their capital. Eventually, Burry's analysis proved correct: He made a personal profit of $100 million and a profit for his remaining investors of more than $700 million.[6] Scion Capital ultimately recorded returns of 489.34% (net of fees and expenses) between its November 1, 2000 inception and June 2008. The S&P 500, widely regarded as the benchmark for the US market, returned just under 3%, including dividends over the same period.[6]