In the case of Spacex that's literally not the case, when private investors bought shares the company was already a decade old and had a single class of shares. It's only since the IPO that the company switched to a dual structure, multiple years after private investors bought in. And class-B shares have only been given to Elon and a few of his friends.

The private investors were free to sue or arbitrage, as it is a private matter.

There were disputes around SpaceX secondary market/special purpose vehicle shares before the listing, but they were all settled out of court, AFAIK.