> Which specific Americans are kind of mediocre academically?

Most of them. We have normalized getting Bs and Cs in our schools. Our school curricula are mediocre, and our culture around education is as well. It is distinctly uncool to care about education here.

> Which specific immigrants are smarter than the average American and are therefore responsible for the nice things about America?

Most of our best doctors, scientists, and engineers are all immigrants. Look at the ethnic breakdown of top AI researchers at the top labs.

> which isn't specifically gated on the intelligence of individual immigrants will improve a country along this metric.

It's not just intelligence. Immigrants overall have more grit, more entrepreneurial spirit, and more ambition and willingness to succeed than median Americans. It takes a lot to uproot your life and attempt to make it elsewhere. The vast majority of immigrants I've met embody the American spirit far better than most born-and-raised Americans I've met.

> And in fact the US has a huge number of legal pathways for immigration

That we are making harder and needlessly painful, which will in turn reduce the amount of highly intelligent and capable immigrants we get as well.