I'd say recolors make a huge difference. Twilight Drake is one of my favorite mounts, but I wouldn't be caught dead riding Experiment 12-B.
But to tackle those points with recolors not making a difference:
- Scarab Lord mount is comparable to the blue archaeology mount, sure.
- Corrupted Ashbringer is more than a recolor of the Ashbringer. Most notable is the circle on it that becomes a skull.
- MoP CM sets are only recolors for... 2 (?) classes. The rest have pieces which are different models.
- Some Naxx40 weapons returned, but there are definitely others which even to this day, have unique models. Take the
staff that dropped off KT for example.
And yeah, ring was just a point that Blizzard does like to permanently remove things.