Magic dragon is not a terrible hero just not great. Not bad having around for expo.
But anyway you can use super weak hero in first and fifth stages sometimes second and fourth. You should get at least 5 to 7 wins daily even on luda doing this, so completing that part of the quest is only gonna take 4 to 5 days max.
Also it is one of the only part of quests that actually requires skill, so the Expo stuff I think is one of the best types of legendary quests. I also think more contest points should be given for the Expo battles because again it is one of the only things that takes skill in all of the game's contests