Hades has never been much of a challenge to me. Ozma bothers me if only because he's so random in what attacks he uses. Sometimes you will hardly stand a chance at level 70, sometimes he'll be a breeze at 40. Did you steal all his good items? That adds to the challenge, and the items are certainly worthwhile.

Either way, I would agree that the optional bosses in this game aren't as good as in many of the other games.