> If you like, name a wealthy American who came from royalty. I can't think of any.

You can play the opposite game too: name a wealthy American who did not come from a multigenerational-upper-middle-class background (i.e. someone who's parents and grandparents were all well above median income).

Of the big names, the only one I can think of is Bezos (his adoptive father was an engineer, but a first generation immigrant with no established wealth). Everyone else, all of them AFAICT, came from backgrounds where they never had to worry about money or support through the early parts of their careers.