My point was that in this alternate hypothetical world, there likely wouldn't be the large number of US domestic R&D companies to serve as valid targets for such investment, as many of the clever people who start them or staff them wouldn't live in the US. Those people would instead be starting and staffing those companies wherever they did live — or in whatever country they could immigrate to instead of the US, with that country then supplanting the US's role as a global R&D center. Which would put American investors in the same position that other countries' investors are in: having money, but few domestic R&D companies that aren't already plump with cash, while most opportunities are foreign.

(Or, if we really lean into the "alternate history" bit, then the US might not have so many rich investors to begin with, as those investors would have been the ones living in that other global R&D center country, who became ludicrously wealthy when their investments into the domestic R&D companies in that other country bore fruit.)

Yes, I know; but we're talking about what would happen in a hypothetical world where US R&D innovation mostly stops happening, not for lack of money, but for lack of talent; so US investors no longer have any interesting domestic options that are likely to bear any fruit at any multiplier they'd be interested in.

Sure, investors could just park their money in what few dumb domestic options there are. That's the "patriotic" approach, and in less-aggressive markets, you'll see some investors [esp. big institutional investors] building the hedge parts of their portfolios out of these kinds of investments. But when the only domestic options are dumb/boring, any "smart money" investor will either take their money and leave the country for greener pastures, or they'll pick up the skills required to play in foreign markets.