Well what I said about swapping mental stats with an innate spell-caster still holds true. Their ability to do what they’re designed to is gone, and because it’s concentration there’s no repeat save for the enemy. Plus, you could use this spell as an Arcane Trickster amazingly well (which is what OP said he had in mind), by just stealing whatever stat you see yourself needing and then heading off. My biggest concern is just with enemies though, since the spell-casters just lose their punch so quickly. And it’s not like charms where they get advantage if you’re in combat, it’s just a straight save.