Accessing Teller of Secrets at level 3 is a symptom of a larger problem. The larger problem is invisibility allowing you to go anywhere and do anything.
I enjoy that I can do that, I really do. I like the freedom.
If you do not enjoy this mobility ... well, you are not forced to go invis and ruin your own game!
Apparently I didn't clarify enough.
I definitely like the mobility. I don't wish to convey the message that getting Teller of Tales by level 4 should be impossible (level 3 probably should be impossible, just off exploration XP), because I think it should be
possible -- very key word there.
The problem, like I said originally, is how good invisibility is. You said "don't use it if it's too powerful," and that particular argument is nonsense. It should be possible (that key word again) to get Teller early and profit from it, but it should not be as easy as it currently is. It should involve far more micromanagement than it currently does, and far more worrying about getting into fights you're sure to lose.
There need to be monsters which see invisibility. Not every monster should, but there should be some, and they should be key watchdogs you'd have to manually sneak around even while invisible. Invisibility should still be good for minimizing the amount of detectors you're actually dealing with. Good spots to put these, in regards to the thread topic, would be the fire-elemental-type-thing near the Burning Legion road, and the Source Abomination in the Cove. This is just enough where you can't just coast through things on autopilot by using Walk in Shadows whenever you see a threat in the distance.
Other than that, the only real change for Teller of Tales should be that the portal in the Silverglen Chapel Cellar should not activate until you flip a switch or something in the cellar itself. It's currently far too easy to pick up 2 Blood Stones by taking the portal backwards, from Sacred Stone to the cellar. You should be absolutely required to kill or pickpocket Loic in order to access the cellar (where you do this is still up to you). It's also worth noting that the devs did not anticipate this and that the Immaculate Trials quest breaks (cannot be completed) if you access the cellar before you kill Loic.
I'm against "one set of books per playthrough." It should still be per level. Yeah, it's OP. What of it? It can be fun, and it can be cool. Cool and fun matter more than balance.
So seriously, I'm not against having fun and very powerful rewards in the game which can be totally out of proportion to normal play if you access them early. This isn't a player-versus-player experience, so that kind of balance isn't necessary. What I am asking is that acquiring those rewards has some kind of higher skill element, where even if you know what you're doing there are some cliffhanger moments of high tension.
