There’s been many comments about the xp and gold ratio in the game.
Award xp based on monster level instead of the standard per room. Beating 2 lvl 1 kobolds should not be worth the same as a lvl 7 ogre. Even just 1 xp per level with extra for leaders and bosses would help.
Award xp based on number of fees. 5 orcs vs 2 orcs should give different rewards.
Award gold per room in challenge mode same as story mode. Gold = xp same as story mode. A slight boost in xp and gold would go a long way on the grind to get from one level to the next at higher levels.