At least some versions of Superman generate/radiated vast power when using their powers. Luthor (& others) have found ways to use that power for their own purposes. Luthor created armor that was powered by that super-energy. With that armor Luthor was able to fight Superman on around equal terms. Most objects created by magic seem to be ineffective against Superman, unless they are powered by magic. Magic seems to be the ability to manipulate certain unspecified forms of energy. What if the super-energy Superman generates is close enough to magic, that magic users (& magical objects) can use it against him?