There is a fundemental issue with the idea that the demons/ devil can be good-natured, but slightly flawed characters, who can do tremendous good given a certain circumstance. And that heaven, angels and god would be hypocrits/ evil/ heavily flawed characters. The fundemental issue in this setup is that you don't actually do anything. You think you are subverting expectations and creating some moral dilemmas, but in reality you aren't. You are just lying to yourself and the readers. Those that whisper sweet lies and don't want you to be happy are the demons. Even if you, as an author, specifically go out of your way to portray and call them angels and god and all, in the story, they represent evil and are thus the demons. And the opposite is also true. The "demons" are the actual metaphors for the angels and god. They are the ones that give you the tough battles to fight and the tough burdens to carry. But if you manage to carry on and keep yur resolve, they are the ones that are the happiest for your success.
So I think what I am really trying to say is that the author and most readers of this trope, do not understand christianity and the bible. This isn't necesarily a bad thing, you can write, and enjoy stories even with flawed understanding of different topics.