SpaceX's market debut sparks debate on how stock indexes should include mega-cap newcomers. Nasdaq added the company, while S&P 500 held back, highlighting differing approaches to growth versus conservatism. This divergence could impact investor returns as more AI giants prepare to list, raising questions about market representation and risk management.

Nasdaq changed its rules to allow some huge companies to join its Nasdaq 100 index after just 15 trading days.

SpaceX's market debut sparks debate on how stock indexes should include mega-cap newcomers. Nasdaq added the company, while S&P 500 held back, highlighting differing approaches to…