> When America was truly at the top of the world in the 1950s and 1960s, it was under 10%. A high fraction of college attendance is better correlated with the 21st century decline in America's situation.

I think this is a textbook example of correlation not implying causality. The US was awarded a unique competitive advantage with WW2, which allowed it to become the world's hegemon. Much of the reason that the US was able to preserve it's status was how it managed to leverage that competitive advantage to fuel it's economical and technological development to build up and retain a competitive advantage. This was only made possible by its investment in higher education and R&D, which is a big factor behind the progress in the 1950s and 1960s you're lauding. Things like the GI bill are renowned by the huge impact it had on the tech industry.

https://en.wikipedia.org/wiki/Arthur_Rock

https://en.wikipedia.org/wiki/Eugene_Kleiner

The US never managed to shake off its anti-intellectual bias, and has this irrational belief that ladder-pulling is somehow conflated with the cream always rising to the top, but if anything it's preventing their domestic talent from fulfilling their potential.