There are also other mounts from raids

What's the matter? You were able to distinguish different shades netherwing, yet they were all of the netherwing faction - 1 reputation. Glad mounts could be WOW Classic Burning Crusade Gold armoured netherdrakes. There are two sources for netherdrakes.

The skytongue mounts , as well as the kara mounts were also offered. With the exception of the kara mount which was a stallion with fangs, the other mounts had distinctive models.

Ok look I feel you. For real I get it. Also, the TBC reps are/feel meaningful. Do it once, and you'll be able to access the heroics you're looking for. You'll get crazy items if you do it again and this is why certain items cannot be replaced easily.

Exactly. When you get the Frenzied Feltalon, it feels so freakin' underwhelming as it's just a redo of two mounts that you already own. The mere difference in color does not make up the enormous disparity in difficulty. With so many different colors for certain mounts just sorta blend together and it doesn't matter that it's the difficult or the freebie, since when their relationship is close that the value of the crazily difficult mount actually decreases, because the freebie mount's value cannot increase even if it seems like a rare one.

There are many recolours of these available via other methods. Then there are all the drake mounts from WotLK and Cata which are just recolours of rare spawn drops/reputation/achievement rewards.

There are also other mounts from raids that I haven't included. Glacial Tidestorm is from mythic Jaina that is a skin of the shaman-class mount. Ny'alotha Allseer originates an ancient mythological N'Zoth, which is just an reskinned jelfish mount.

What you mean by "reskin". The mythic mount of N'Zoth is simply the mount for jellyfish, Jaina mythic is just the shaman class mount, Gul'dan's mythic mount is just grumpus mount (I think at least) Shackled Ur'zul, from mythic Argus is (I believe) the gryphon's skeletal mount that DKs have.

Archimonde’s Felsteel Anihilator is the only mythic mount that I can recall being "original in the time". The Sylvanas mythic Mount is also a different type.

Recolours usually refer to swapping of textures. I'm not entirely sure what the definition actually means. It's definitely easier to cheap WOW TBC Gold change the color of than other things you can imagine, all you have to do is the slider alter the color on it and call it a day.