Per the S&P 500 website, the claimed subset of the market is "U.S. large-cap equities". S&P claims their index is "best single gauge of U.S. large-cap equities". But, it's clear that given the current iteration of the rules, none of the major upcoming IPOs of Spacex, Anthropic, or OpenAI are eligible for S&P500 inclusion, and they likely will not be for years.
Claiming to have the "best single gauge of U.S. large-cap equities", yet having rules that exclude three of the top 20 largest U.S large-cap equities which make up ~5% of the total market cap of the U.S. stock market, means your benchmark is inaccurate by my book.
"means your benchmark is inaccurate by my book.", and like The Dude says "Yeah? Well, you know, that's just like uh, your opinion, man."
Create your own benchmark, and you can say it is a subset of "U.S. large-cap equities" and "best single gauge of U.S. large-cap equities" and let the market decide who does a better job.