But the heroes are stronger,.... Play this map:
stronger.zip
I just put the heroes in a room against the evil creatures, gave the creatures a numerical advantage, and still the creatures get slaughtered by the heroes. And of course I did not include the avatar.
And I'm sorry, but I'm not going to replay the Good Campaign, I've already played it before and I would change more. But I do like how easy it is in Dungeon Keeper to modify creature stats and give them new spells and abilities. There's nothing unorthodox about proposing different stats, many people have and all of them are different.
You can never get the dwarf to work properly as an imp though, it will just not function no matter how you set the jobs, too much is hardcoded. The only think you can do for the good campaign is make the imp give all the sprites and stats of the tunneler. And turn tunnelers into imps.
EDIT: Play it with the original or KeeperFX stats of course.
I made screenshots. Before the fight:
And after the fight:
Notice how 6 heroes survived.