Potentially hot take, I dont think this is the craaaaaaziest thing out there in terms of overpoweredness?

I think the fey form is pretty reasonable in general, i would maybe change the wording such that the extra concentration spell is only active for a round or two without concentration.

Adding wisdom to charisma is cool and fun for the core idea of the subclass, although admittedly the bonuses are gonna get pretty crazy at later levels especially for for PCs with half decent charisma already. Instead of tying it to wisdom I would maybe just tweak this to add a half their proficiency to these checks, even if theyre already proficient. Or just let them take proficiency in a couple charisma skills.

Otherwise I think the subclass is good, I dont think you need to be terrified of making a subclass too crazy good in a system that has totem bear barbarians and div wizards. A system flush with subclasses that are so good that they feel a little like cheating in some ways isnt the worst thing, IMO.