Ditto to the therapy fields, they will not be replaced by robots or assistants for a while - they pay well and the years of training are shorter.
But for pre-med if he is not “getting” the math, more books and self-study are not gonna help without a tutor, maybe even both a math tutor and a test tutor. Then if he still is lagging, maybe further reflection will be needed.
Some people are just poor at taking tests. On the practice tests, the time limit needs to be as rigorous or more so than the real exam.
He could always get his maht credits at a local community college that will transfer credit
Here they can do that while still in high school
If he has to take all the remedial classes at least they’re cheaper
Bu if he’s a bust at math- maybe he needs to broaden his career search