I'm really appreciating seeing the difference in species. Demons use human connections (empathy, family bonds, loyalty) as weapons against them, and their perception of the world is completely different. Elves, from my view, aren't all that different from demons when it comes to not making close bonds like humans do, so I think that's why Frieren actually has a better understanding of what the demons are doing. She knows that they have no intention of playing into human values because the first humans she truly understood were in the Hero's party, and she still thinks humans are strange. I'd also bet that one of the main reasons why she wants to protect the town is because the heroes would have wanted to protect it. Before she met them, she probably would have thought it would be too much effort, and would only attack the demons who attacked her.
It 's really nice to see a fantasy writer--in comics, books, manga, etc--who understands that just because fantasy species look similar doesn't mean they are the same. And if they are the same, there should be an explanation for it. Demons aren't just humans who can shapeshift. Elves aren't just humans who live long. It's so refreshing.