Tbh, that tail looks totally fine to me

I can see the problem with the lips (pixelated edges) but this is the first time I ever see something like this. Is it possible the person you got that screenshot from is just playing on low settings or something?
In general, the character models seem very high quality, sometimes painfully so...which brings me to my real gripe - overworld textures

As long as this is the overworld, it would actually look less jarring if our characters generally had low quality textures too..