If it becomes a part of some peoples builds SO WHAT? The builds this opens up are hardly overpowered. In fact, I'd argue that most of them are weaker than just building a wizard with high intelligence and spending a few level ups on raising it to 20. The headband allows a few meme builds, but mostly people will use those to have a little fun with something weird (like maybe roll a really stupid half-orc that "just happened" to find the headband and become a wizard).
I suppose you could use it to make an eldritch knight with decent spell attack power, but that would probably still be weaker than a battlemaster.
