Gosh no. Gliding mounts would be okay at a stretch, but flying mounts ruin games.
I would settle for gliding. I loved how Legend of Zelda: Breath of the Wild integrated the glider. There are so many spots in ESO that would make a good jumping zone. Or in major cities xD players already jump from the top, how about you let us glide, so our mounts dont take so much dmg... gliding mounts, that is.