I might be pulling things out of my ass here but IIRC the correlation is up there with that of your parents’ wealth. And in current political discussion lots of time is spent on how to deal with the latter. It may in fact still be a weak predictor, but that obviously doesn’t make it meaningless.

I'm having trouble parsing this - is it a mark of stupidity not to believe in IQ or is IQ a lie that mostly hoodwinks smart people?

Please stop. Your self pity is annoying. You have an engineering degree. There’s no way you’re not in the top quintile of intelligence and you’re probably in the top decile. Enough of the pity party. If you hate yourself go join a boxing club or start running marathons or something else that will put the petty bullshit of work life in perspective besides the fact that you’re young and you have a beautiful, working body.

First, understand that IQ tests can be biased and can shaft minorities. Second, they are tools and are only as good as the person making use of them.

Third, eat right, exercise, live right, etc. Performance is impacted by health and even supposedly high IQ people will perform worse if they are sick, short of sleep, etc.

IQ isn't a useless concept, but I'm somewhat well versed in the history of IQ tests, etc, and it's got a lot of issues with it.