Yet our current society tends to consider it completely fair that success should be a function of IQ.
IQ is no less a given than face symmetry. Grit too. Nothing's "fair".
The switch you've made here is between "success" and criminal punishment.
IQ has a pretty strong correlation with the quality of the work you can produce. Higher IQ is generally beneficial to the solution of any task. If you are trying to go to Mars or find a vaccine for COVID-19, you probably want very smart people in the room. Hell, you want smart people even if you are building yet another ecommerce website.
The same is hardly true for beauty. Excluding beauty-specific jobs, skills and experience should always prevail over look.
IQ: unfair to the individual, justified by society well being Beauty: unfair to the individual, no particular advantage for society
No, it's not. Using any criteria that creates substantial disadvantage to a protected class is illegal if you can't show a sufficiently close nexus to bona fide job requirements/performance, which happened to be found to be the case with the IQ test that was adopted as a direct replacement for overt racial discrimination in the Duke Energy case. But the legal rule that comes from that case is not “IQ tests are illegal”, and in fact IQ tests are used in a number of places in hiring (including, as became notorious in another case where the practice was upheld, being used where a score above a threshold was disqualifying in a particular police department.)