Imagine having to wait a week to see the MC pounding this demon for 3 chapters straight :v ...
While I understand the MC has a lot of resentment for this guy, it got also dragged on for long enough. And going: "I had fun killing the other demons" is just redundant at this point. He showed he was on top, get over with it.
I really dislike it when a seemingly sane, level-headed character gets turned into an actual villain just for the sake of edgy writing, to show: "How wronged and angy he is".
There's a difference between lashing out in anger, being highly violent because you were violated and wronged, but it doesn't need to cross over to torturing your abuser.
Imo, the MC should've stomped on him a few dozen times, dead-space-esque, to the point his head is a puddle of blood and nothing else, and be done with it.