World Difficulty, Heroes, Experience and Risk vs Reward
I'm slowly starting to form a Theory about an issue in the game, which may be obvious but I haven't seen it discussed.
The apparent symptom: People who play on higher difficulty seem to be the most vocal about how heroes dominate the game.
There may be many reasons for this. It may be that playing on higher difficulty forces the player to "min-max" by focusing on the strongest strategy and ignoring the weaker ones.
But there may be another reason as well. Unless I'm mistaken, the primary factor that decides experience gained from monsters is in fact combat rating. Combat rating in itself is a function with several variables, including special traits, attack/defense and... hitpoints.
Example: Banished ogre on Insane with 60 hitpoints: 14 experience. Banished ogre on Normal with 20 hitpoints: 12 experience.
Example: Ogre on Insane with 120 hitpoints: 31 experience. Ogre on Normal with 40 hitpoints: 22 experience.
So... higher world difficulty causes monsters to be more difficult. More difficult monsters are making the experience (both available and gained) greater. Higher level heroes is a big issue because it upsets the pacing of the game and the balance of heroes vs other elements.
Suggestion: Experience gained from Combat Rating should always be modified as if the enemy hadn't been boosted by difficulty. This is intended to stop the circular logic behind hero experience in high "world difficulty" playthroughs.