I created just such an enchantment based NPC villain for the game I am running. He came from a very prominent White Council wizard family but never developed the ability to throw around evocations. Making him the first in his line for generations to not serve as a Warden. However, he is very smart, very disciplined and a heck of a Thaumaturge.
Regardless of the history; he is a submerged level, 9-refresh character (still has one refresh left). When you concentrate like that, yes, you can very nasty at what you do. And he is. Especially with a good, paranoid GM controlling him. He is, though, not unstoppable or, in my opinion, broken. He has his weaknesses. Namely, he is no where near as flexible as the PC wizards. Potions can give you some flexibility, but they are limited.
Right now, he knows more about the characters than they of him; so he has been able to control circumstances and keep the "Home Field Advantage", so to speak. But, as soon as he looses this, he's in big trouble. Making magic items takes time and effort. Swapping out your slots is not something done over night. Plus, items can be stolen or destroyed; all the easier to pull off as they are readily apparent for what they are by anyone with supernatural senses.
Crafters are not broken. It just takes some intelligence to beat them, not just a good stat block or die rolls.
If your opponent learns what your items are and their capabilities... you are in a bad spot.