Hint: There are humanoid aliens.
There are a lot of elements of fantasy IMO in Avatar that fall outstide of the scope of ST type sci-fi. e.g. flying dragons.
Large flying predator =/= dragon.
And there is nothing wrong with humanoid aliens. We're humanoids and we obviously exist, so why could life on another planet ALSO develop a humanoid?
So the assertion that avatar is full of "fantasy" fails. Every "fantastic" element of Avatar has a solid grounding in either actual science or is an extrapolation using science.