a student with an IQ of 80 is incapable of producing the kind of work Thomas routinely produces [...] I'm skeptical whether many 100 IQ students could create a career path like Thomas's path.

No one's denying that. The "race realists" claim not that all black people in the US have an IQ in the 80-90 range, but that the average IQ of black people in the US is in the 80-90 range. That's perfectly consistent, as gwern said, with plenty of those people being very smart.

Clearly you don't get onto the Supreme Court without being distinctly cleverer than average. For all his negative comments about Clarence Thomas, gwern is not (so far as I can see) denying that.

That's relevant to the argument because the number of "black swan" high IQ people we observe should be related to the mean IQ of the population.

Yup. But "smart enough to be on the Supreme Court" doesn't seem to me like black-swan IQ, even in a (real or hypothetical) subpopulation with an average IQ in the eighties. Unusual, sure. But well within the range we should expect there to be plenty of.