Well, if you're including "anyone who sells things to schools" in academia- then yes, my argument doesn't really make much sense.

But, for the sake of steel-manning, let's pretend that instead of meaning that, I meant academia as the broad collection of things typically associated with it - formal schooling, tenure, teachers, students, classes, etc. Even if you include textbooks as a NARROW part of academia, the point is that you can forgo all that other stuff and JUST take the textbooks, and still be told basically the same things.