Having worked with many top tier graduates from many top schools, I think we need to dispense with the idea that academic performance is determined by intelligence.
In my experience it was highly correlated with work ethic, many top tier graduates would come in with a push to work exceptionally hard. Sometimes they’d come in with an attititude that they’d “made it” and not work hard enough.
I don't think that is what science agrees with. IQ correlates pretty strongly with educational achievement. You can disagree with IQ all you but one thing it pretty surely doesn't measure is work ethic.
I went to a top tier high school and a top tier university. At a top tier university, in STEM at least, the fraction of students who had both high IQ and could work incredibly hard was noticeable. The fraction of STEM people who could get an A without working hard was low to nonexistent.
In my experience it was highly correlated with work ethic, many top tier graduates would come in with a push to work exceptionally hard. Sometimes they’d come in with an attititude that they’d “made it” and not work hard enough.