I'll admit it was incredibly jarring (for me) to experience Frieren outright say demons are 100% evil, cannot be trusted, and must be exterminated with prejudice. But what you say really is what makes it interesting. We're so used to media humanizing villains in fiction that we just expect it at this point.
Flipping the trope and trend makes it novel again.
Could it be Sharkronomicon: Dawn of the Divine Invocation?