I do think it's counter-productive for America to make it harder for legal and talented immigrants, and we should fix that - but what's your evidence that America isn't still the world capital for the ambitious?
Statistically: The close competitors (e.g. Western Europe, Canada) are looking pretty dire economically compared to the US.
Anecdotally: I have friends from Estonia, Canada, the UK, and France that are all clamoring to be in America for the opportunity.
Historically: Post-WWII in the 1950s, 6.9% of the population was foreign-born. It's now 15.8%. So are we really more closed-off than we were then? Or is this just the response to the ever-increasing interest in immigrating because of the US being as compelling as it is?