Thankfully, I also work in the adult world and this world requires judgement.

As an example, my wife is a physician. She and her colleagues use metrics to help assess a patient, but ultimately treatment is based on their judgement. Purely relying on hard numbers, such as what an EKG gives, would lead to dead patients. Many of them. I am a mathematician. My world revolves around hard computational numbers, yet my algorithms will often given misleading results. Determining when that is requires judgement. Despite a push too the contrary, good hiring managers assess applicants and take responsibility for both good and bad hires. This requires judgement.

And, yes, I can also find examples where someone either didn't study or used a book and did well on their SAT. That said, in person test prep with a tutor absolutely has a large, positive effect on test scores, much more than simply a book. Kaplan has the internal data. It's absolutely worth the money if one can afford it. Most can't.