It's a ridiculous excuse to make mounts impractical of flying able to fly just because it's a fantasy game. There's limitations to what kind of fantasy are we talking about.
SE should just leave mounts incapable of flying as is. Also no, I highly disagree on making characters fly on their own.

I just hope SE ignores ignorant requests to make land-only mounts like Sleipnir, Fenrir, ARR Beast Tribe mounts etc. able to fly.