A slur is an insult. I'm engaging with your argument but you keep changing why it doesn't work. First it was pointy ears yet we've established Elves have pointy ears. Then you said Tolkien didn't humanize the elves even though they are almost the same species. Then it was there are not racial tensions in Tolkien work to have slurs. Yet we know that isn't true because we've seen racial tensions shown.
The thing is though that Tolkien was trying to keep vulgarity out of his works. So he made things more poetic when they needed to have insults. That however doesn't mean that the culture and society function with out the vulgarity only that it wasn't important to his story and something he was trying to avoid to set his work apart from others of the time period.
A slur doesn't require pointy ears to be a negative connotation. It only requires that it could points out something "different" about the target. https://en.wikipedia.org/wiki/List_of_ethnic_slurs Most of the slurs on that list wouldn't work based on your narrow definition of a ethnic/racial slur. What makes it a slur is that it is calling out something only that group contains. Which is why ABC could be a "slur" to insult/demean American Born Chinese people.
It is laughable that you think a slur can only be a slur if the target "exist below" the one using the slur. Knife-ears in Dragon Age isn't even a reference to their heritage, social standing, or anything else. It is simply because their ears are pointed, like a knife, and it sets them apart. So calling that characteristic out and using it in a negative fashion makes it a slur. It is why groups in the real world have "reclaimed" words or terms to repurpose them from a slur.
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I think it wasn't that bad but the "young" or "baby" warg look was definitely a problem. But I don't think the scene would have worked the same with a full grown adult warg as they seem like they would be to powerful to lose. Though it is possible these are "ancestors" so look slightly different.