This argument would hold up better if FFXIV had an overabundance of glamour always thrown onto the Mogstation. But it doesn't. In fact, many of the most popular glamour outfits, mounts and minions can all be earned in-game without spending a dime extra. Look no further than the Rebel Coat, Dalmascan top or the Ao Dai. People wore those (and still do) more than a good chunk of the cash shop dresses.
People keep bringing up this extreme scenario, insisting that if we wait long enough, SE will inevitably put everything good on the Mogstation. Six years and counting, they still haven't yet. So either they're extraordinarily patient or they've found a compromise that seemingly works for most players.
Now I get being disappointed you found something you would have preferred earning in-game. But saying it shouldn't exist at all comes across selfish. To spare your own disappointment, you're essentially saying "If I can't get it in-game, then no one should have it at all." I bought that Carbuncle mount the day it came out; two actually since my BFF adored them. So I bought her one as an early Christmas gift. We both got plenty of use out of them, and I don't regret my purchase. Was it overpriced? You could argue that. So is going out to restaurants, ordering take out or having a commission done of your character.
Some people are content spending extra money on luxury things simply because they can. There isn't anything wrong with it.
Bringing that back to video games. Like said, the cost of development has skyrocketed over the years. If micro-transactions didn't exist. We'd be paying a lot more to play those games. I dunno about you but I prefer the option of buying novelty cosmetics once in and while or the sub fee being $25.