Well the public and private school system which the vast majority of youth in the US take part in has mechanisms for identifying the gifted. Those who excel in school generally go on in life to better themselves.

Most people are not profoundly gifted, so the majority simply do as well as their parents, give or take.

I don't know, wouldn't be so sure without actual supporting data.

Anecdotally I know many talented people who got "broken" at high school level (due to any number of issues, from poverty to physical and emotional trauma). Having connections, mentors, initial capital, educated family, it all helps a lot.

This is not US-specific either, I made it to the US from a war-torn country across the globe with no money or connections, but I am extremely stubborn. There were definitely people who didn't make it this far who arguably had the pure IQ advantage.