There's no such thing as whining.
Feedback is feedback. I know roguelike devs have a reputation for being evil, and I'm probably not an exception... but, I still have a certain goal in mind for the level of challenge Demon provides, and I do want to know about and fix it if it goes over that.
Besides, as it happens, I agreed with you even before you posted.
I already plan on making some small adjustments downward in corpse difficulty in the upcoming build. I still want them to be quite dangerous... but I agree that they've gotten slightly meaner than I intended.
Main things that will probably change (some or all of the below):
1) Prevent excessively high level "rare" monsters from a level from being among the corpse spawns. This one is the most likely to happen.
2) Not going to let any of them move before the player anymore.
3) Possibly will reduce the number of demons that spawn by 1... less certain about this one. If I don't do this, I will probably do something else that reduces general difficulty instead, like reducing how well corpse demons' levels scale up to yours.