Absolutely. You should definitely have hard limitations on a form like that otherwise it's a walking cheat code. Have them lose access to the form at a critical moment but to outright lose? That would make no sense at all.There are legit ways to make fusion not a easy win, like the time limit. Jojo, One Liece, Bleach all found ways to make that much power a double edged sword.
Problem is Tori-yams doesn’t give a fukk.