Counting from every game where the devs did something like this with anything ingame,Basically, if someone had a purpose to run those Dungeons now he/she can just wait till he get the writs..The thing about it is, the Legendary mounts available for 4 reward writs are different from the dungeon Legendaries. With the word "Light" in front of them, I'm thinking they're either significantly nerfed, or they are now recognized as a completely separate mount. This would mean the players who exchange their writs for one of them would not get any collection addition to their bestiary, and they also won't get the title (although that was always the case with writ mounts).
After a world full of Letonsia we'll have a world full of Legendary Skins mounts. In short what was supposed to be a goal it's a mere "wait a bit and I'll give it for free".
Ofc I'm glad that some players can have such beautiful mount, but what now? I was planning to buy a recipe for crafting my own legendary marks, but for who? And for which price if players can just wait and have the same skin?
Dunno what to think about this move.
It may also be a way for players who actually worked for the achievement of taming a legendary to keep their uniqueness.
However if they are getting them just for their appearance, everything I've said is null and void.