@0neDragon You have to remember, the curse was literally killing him whenever he used magic. Basically, whenever he used magic, it would take away from his HP permanently as well. He was failing C-class quests because he had to stop using magic, but couldn't develop any other skills needed to not rely on magic, like swordplay, archery, etc., because the world still relies on classes and the skills that come with them. He was a sorcerer/magic-user, so he couldn't use physical skills properly.
And in general? Even before, it is indicated he was fucking OP, because he was able to remove the curse from his (now)daughter that, given indication, shouldn't be possible to remove.