This has somehow become the standard wisdom, and it's just wrong. IQ is highly predictive of a wide range of outcomes; see for example https://www.vox.com/2016/5/24/11723182/iq-test-intelligence.

That's just correlation, which could happen even if IQ is really just a function of your socioeconomic environment or other things that are not actual intelligence. Although there is strong evidence that is not the case.