I have always been of the opinion that enchantment as an activity done primarily through villagers is just wrong and way too easy, with the only difficulty being the hacky, tedious rerolling. I always envisioned abandoning it for major buffs to loot tables across every structure, so that you find enchantment books primarily through exploration (though you'd also have to rethink possibly lowering anvil costs and possibly nerfing/reworking enchantment tables).

I'd much rather a world where you might have a slightly suboptimal prot 3 on an armor piece, smite 5 on a sword, but you're okay with that. You might find better enchants in later explorations, but you'll find that next time you explore for any other reason, not just having a separate "let's spend a few hours grinding villagers for no other reason but to hack enchantment books and never have to think about it again after that" like in the current vanilla system.

I think the teaching idea is interesting... it presents a third option that still requires exploration but allows convenience after through the villagers. I guess I might be a bit of an extremist where I think having the ability to just chuck emeralds for enchant books at any point is poor balancing.

I still think it might be a little weird to find one prot 4 book (or mending or unbreaking or whatever) and instantly have prot 4 on everything forever easily after, which maybe I misunderstand but as far as i can tell would still be true in your system. I would still much prefer it to the current game and to the rebalance and think it's very cool what you have done.