Why not cite a study favoring your claim directly rather than challenging me to? What does fluid intelligence predict besides math success? If it predicts more, there should be studies on point.

Are you challenging me to find a single study using a matrix test which predicts to any degree some metric other than math success, such as income or employment or highest attained degree, and that's it? Are you sure? Because your following restatement agrees that matrix scores can be predictive outside math.

I'm not saying matrix tests don't predict anything but math achievement; rather that fluid intelligence adds nothing to prediction beyond what a general IQ test provides, which is to say, a bit more precisely, its other correlates with achievement can be accounted for by a combination of other factors. That's a lot stronger than your "reasonable" position--which I'd call a trivial position--but weaker than claiming fluid intelligence measures are useless for brute prediction outside math. They have no value outside math prediction because other tests are better for other predictive purposes.

I think we have different views on what is "valuable" (eg. is a matrix test faster and easier to administer than your combo of other factors? Then it could be valuable even if it's not quite as good a predictor), but your stronger position does not seem obviously wrong to me, so I won't object to it.