Yes I used a extreme example but did anyone of us truly believed a few years ago that we would have such a huge cash shop and that we would lose our veteran rewards (one mount since then was all we got..), that we get jump potions or that we soon will have an app that has a sub fee + coins in it? I honestly did not. I believed that there would be at least some borders that they would not cross but thanks to quite some decisions I honestly can see them doing much worse then its right now. And with your argument you give them free reigns to do exactly that.
Its their product but a product is useless if nobody buys it anymore. So no they cant do whatever they want with it because there will be a time where even you and others will say "its enough". And then it will be hard or even impossible to get the good will back. Honestly I have learned enough in my study that money alone is not the most important aspect for a company anymore. To survive on this market you need more than being greedy. Look at EA. They have ruined their reputation so much that people are completely skeptic about their games. They are still earning money but how much more could they make if people still believed in them?
The problem with "its only fluff items" is that the endgame of this game is owning fluff items. How many people are running a lot of stuff only for the rewards? Why could they not have put Sleipnir into the Odin trial? Or the carbuncles? Why do they had to land in the shop while people are already complaining about not having enough to do? When its the fluff items that play a big part in keeping lots of content alive, then it does hurt the game to just put certain items into the shop. Because each exclusive one could have been a ingame reward. (And lets not talk about the manderville costume..who could have been something for Hildibrand ingame)
In the end mount, pets and other stuff are important for quite some people. So they have the right to complain when something like that gets locked behind a pay wall again..exactly how people would have the right to complain if they lock other stuff behind the pay wall.
(And honestly I still find it funny to read some posts here that state how its just luxus items and its fine that they are in there, but at the same time some of these people also posted against the app fee and the coins. x) I am not saying that one could not have different views on these topics, but its interesting how the coins that are also theoretically not hindering you to play the game are a big No no for them, but cash shop is fine.)