If IQ was one of the best predictors of job training success, it would be used everywhere. Instead, very few companies use it. There's a persistent myth that IQ isn't more widely used because of legal concerns, but that can't be right, because IQ and general cognitive tests are used by several of the largest companies (with the deepest pockets for discrimination suits) in North America --- and, further, the Griggs v. Duke jurisprudence that roots the myth doesn't have any force outside the US, where... IQ testing is not generally used in employment.

I don't know what the "self-assuaging fantasy" is supposed to mean, but you can read Cosma Shalizi to see how any set of tests structured like IQ tests are necessarily give rise to a "g" fact, even if you randomly generate them. I feel like I don't have to assuage myself too much that math works.