The economics of college vs. the economics of private tutors (2020)
marginalrevolution.com
marginalrevolution.com
It doesn't factor in the network you gain from college, chance to collaborate with others, opportunity to find romantic partners, etc...
There were also originally more than a dozen GRE subject tests, but with the discontinuation of the chemistry subject test this year only three remain (math, physics, psychology.)
Plus, it's easier to accomplish when you absorb yourself in one topic, rather than 3-6 at one time. Too much multitasking is unproductive, ineffective, and an easy way to hate your life.