Are you sure gold challenges are supposed to be vicious level? Fighter is easier (they nerfed it), berserker is easier, warlord is borderline, theif is easier, rogue is borderline, assassin is easier, priest is easier, monk is borderline, paladin is borderline, wizard is easier, sorcerer is easier, and bloodmage is borderline. That's 7 out of 12 classes. It also seems that the harder ones are third tier (with the exception of assassin). Most of them are tricky, and fit in between vicious and hard. Heck, some are practically easier than hard.
I speak chaos.