Note that index funds don't hold companies in proportion to their market cap, but in proportion to their free float (shares available to purchase on the market).

Both SpaceX and OpenAI's estimated free float are around 4-5% of their shares at IPO. This means that we really are talking about companies in the sub $100M valuation in term of index fund impact (assuming under $2T for each).

"free-float adjusted" is the key term

5% of 2T would be $100B, not $100M.