Complex sentence: Within the context of the stories, Superman's powers, as great as they might be, are the result of a natural phenomenon, not supernatural, so he's affected by most forms of sorcery in the same way as any mortal.
Split into simpler sentences: Within the context of the stories, Superman's powers, as great as they might be, are the result of a natural phenomenon, not supernatural. As a result, they offer no protection against magical forces, and he is affected by most forms of sorcery in the same way as any mortal.