No, it is no "normal development", if a MMORPG expansion launches, and 60% of its players leave after the first month. An expansion could bring the novelty a new game does. It just does not, as the developers do not know how to do it.
Also, no, FFXIV does not see a massive hype and a massive sub loss.
https://steamcharts.com/app/39210
The last 30 days had have the 2nd largest number of concurrent players the game had since its launch, having december as the best month in history of the game. Even if there are temporary losses, they always stabilize again within a few weeks. The game is 8 years old, WoW did already decline after cataclysm, and was spiralling down after 5 years. Since cataclysm end, the game suffers from sub losses, and blizzard already knew those days it was the casual/normal gamers that mainly left their games. They tried to gain casual gamers back since then but with an unfun implementation of the world content which was never engaging or fun.
Fact is, WoW could be way more successfull if the devs just would get rid of their biggest mistake they started to implement since Catacylsm.. the massive dumbing down of gameplay for the masses, starting at dead dull world content and culminating in LFR being a theater trash version of the raiding game, without character progression, just being there to let millions see the content, to make raids work financially, while every aspect of good gameplay was lost to the developers bad idea to rape the raiding game to be compatible to matchmaking.
Blizzard thought, for some reason, most of the casual gamers would like stupid gameplay, but obviously they had been wrong. Being a casual gamer does not mean you want to endlessly grind mobs which hit like a feather, it also does not mean you want to play a theater mode raid where the best thing you can do is not to troll other players out of boredom, as the matchmade raiding game itself is not compelling at all.
If Blizzard wants to have a large audience of solo players or matchmade group content players, they have to create gameplay for them, and not just copy paste a game component like premade group raids and water them down to a zero-gameplay feature. Games have to be engaing, fun and not just content shows.