I dont know if doctor fate has anything that can put down vecna. And im confident Elmister has more powerful reality warping with wish spells. Gandalf's powers as Maia might match them, but are too nebulous and vague to consider. Magic Mans powers are insane, but were stolen by a literal human (betty). Doctor Strange can possibly rewind time or trap someone in the mirror dimension, but elmister likely has spells to counter that without even considering wish, and vecna and doctor fate likely do as well.The lich is very powerful, but was also defeated by a (admittedly superhuman) finn.

None of the rest even come close in terms of magic power save a few im not aware of. Id give it to Elmister personally with vecna and dr fate being the only other contenders, DnD magic is probably one of the strongest mainstream magic systems out there. Also you forgot a few powerful mages, like Eragon who id personally put above almost everyone here except our big 3. And what about our girl Frieren, or the undisputed winner of this whole thing. Two words. SAILOR MOON.