Same thing.
Invincible recycles a previous mount's skeleton (i mean that with the term 'model'), yet it's one of the most iconic and popular mounts in the game.
And of course the Ren'dorei would share their model with the Blood Elves; they were Blood Elves once, but twisted by the volatile energies of the Void. What model should they use, if not the Sin'dorei's one?