alt Hacker NewsIt may be used as a benchmark, but that’s not actually the purpose of it. The purpose is to serve as a way for people to invest in a representative sample of the market. It can still be a representative sample with safeguards. If you want a benchmark without safeguards, you can calculate one without risking millions of people’s life savings.
You have your history backwards. The S&P 500 was created in 1957 as a benchmark. The first investable index fund tracking it (Vanguard's) wasn't created created until 1976. Vanguard created their fund to track the benchmark, not the other way around.
And if you need a second, different index to function as the true market benchmark because the S&P 500 no longer reflects the actual market, then you just agreed the S&P 500 is no longer an adequate benchmark. You just agreed with my point.