The U.S. had immigration restriction for almost half of the last century: https://history.state.gov/milestones/1921-1936/immigration-a.... During this period, the U.S. became the undisputed superpower. Silicon Valley was established during this period too.

Of course we continued to accept superstars even during immigration restriction, like German scientists fleeing the Nazis. We probably don’t need more than 10,000 or 20,000 carefully selected immigrants a year to continue doing that.