I don't think it's unreasonable at all but, aside from streamlining the toggling, I'm not sure what more you want DDB to do about it.
They can't stop your players from buying their own books on DDB, anymore than the FLGS can stop players from buying books for your pen and paper games. The toggles allow you to control what content you share, and access to the character sheets lets you check to make sure your campaign restrictions are being followed, both of which features offer a leg up on pen and paper games, but beyond that I think you just gotta have a conversation with your players.
Note that you can already directly access the character sheets yourself and change toggles, as well as add/remove/edit whatever you want. Though here I would again recommend a conversation.
Again, aside from making toggling features on and off a bit simpler, like having a set of master toggles for the campaign, which I agree with you about, I'm not understanding what more you are asking for.
I don't think you should be able to toggle off a book that the player has bought independently (would that even be legal?). That would be like searching a players backpack and taking away their copy of the Monster Manual or something. In that sort of situation I think you've just gotta explain what your rules for the campaign are.