Exactly. If the Demons were completely unreasonable, Elizabeth should have been unable to convert them/ convince them to leave last chapter. And Derriere's comments, Nerobusty's coward actions, AND Ludociel's freak smile all make it clear to me that the Demons, at least at the end of the war, were backstabbed by the Goddesses.
The one thing that you all are forgetting is about magic, which was the whole reason this war was fought in the first place. The only reason the Demons would bother to live in peace with everyone is if they have enough magic power to survive, which there clearly is not enough of to go around. The humans are taking it all up; so either the humans go, or the demons do.