Yeah, I really like the ideas of the mages, but the outside towers do feel a bit lacking in content. Like the puzzles could have had a little bit more to them. It's strange that relatively-fit-but-not-a-superhero Garrett can swim through the water tower without even needing a breath potion, when that's supposed to be something that nobody but the water mages can do.
This is definitely the case. It shows up at any boundary between 'rooms', but is most noticeable in doorways. For example, I was trying to see how close you can get to Raoul in the caverns, and as you cross the threshold that triggers his conversation, you hit that full-darkness line, so he must be able to see fish in the dark. I avoid using it unless the space itself is already mostly dark.