every time they add content to the cash shop it necessarily precludes them from adding that same content as a reward to a piece of playable in-game content. I think we can all agree that if this new mount were an extremely rare achievement reward and was also available in Mog Shop that we would be filled with righteous fury.

However, it's perfectly reasonable to argue that the devs only have the resources necessary to create these cool mounts/other cosmetics but not enough resources to actually build new gameplay surrounding each one and that the Mog Shop is a compromise solution. But the flipside is that once we accept the Mog Shop as part of the game's design the devs lose a lot of incentive to try and balance these two things and in a worst case scenario may end up locking too much content behind the store, content that really should be available in game as part of something like DD or a new sidequest or achievement reward.

Personally I prefer to ignore cash shop items, I support the devs with my subscription and I like to think that subscription entitles me to all of a game's content, provided I put the work in the achieve my goals. It does irk me when something prestigious like a rare mount is totally disconnected from in-game performance/achievement. But I acknowledge reality.