I'm trying to answer my original question for Fedran, “why haven't mages taken over the world,” with the concepts of resonance and feedback (inspired by electromagnetic interface). As I worked through the ideas, I realized I was creating a world that didn't have one of the major staples of fantasy literature: artifacts.
Magical swords, golems, and flying castles are a significant rarity in my world because I wanted magic to be dangerous around other magic. Having a reliable tool, even something as simple as a lantern that didn't go out, was contradictory to that and also diminished the impact of the efforts that went into a Farimon Chamber.
On the other hand, I couldn't say “no magical items” because I still am creating a world where I have mecha and giant robots made out of wood.
This also led into some really interesting ideas about felony resistance, why dragons are almost extinct, why the Puzzle King's Castle is such a terrifying place, and how the desire to enslave a single person kicked off a world war (hint, read Flight of the Scions and then read Sand and Bone).