What is incredibly well established is that g is incredibly predictive for many life outcomes from income to educational attainment to drug addiction. This is what IQ test measures.
The only thing disputed is whether g is the same thing as “intelligence”, and the only dispute there is from softer science fields because “intelligence” is a word without a precise definition and a lot of feelings and opinions wrapped up in it.
It does, of course, give you a correct answer if you have the wolfram alpha plugin installed, though.