Wow! This comment inspired me to dig deeper.

After 20+ years in the market, today I learned: "The S&P 500 is a float-adjusted, market-capitalization-weighted index."

So presumably an S&P 500 index fund is not disadvantaged, since it is tracking a float-adjusted index, i.e. the weight of SpaceX will be tiny if its float is tiny.

Or, is there a nuance that I'm missing?