>It's downright crazy to say you aren't learning anything by reading. You likely won't retain that high a % of the content without repeated drilling, but it's not like nonfiction exists for no reason!

How much of a nonfiction book can you recall a few months after reading it? Probably very little.

However, I haven't taken a calculus class in nearly a decade and I still know how to solve derivatives and integrals.

Point being: there's levels to this, and reading is not nearly as effective as drilling exercises.