I know people who started this game last year and they're not even into Shadowbringers. One of the strongest parts of this game is that it's kept most of it's old content relevant, so I don't know if I can agree with this take, the game kind of fails you once you're caught up with everything.
EDIT: My top five
Once you're caught up with the MSQ, the leveling experience is pretty terrible.
Gearing your characters for end-game content doesn't feel very good.
The game won't teach you how to play properly, making getting into extreme and savages feel hostile.
If you were looking to get into end-game hard content be prepared to ask yourself why you're starting on M9S and not on M1S, their hardcore content goes to the bucket too fast.
You end up wondering why is there nothing 'new' to do for months at a time.
There are tons of things new players can do because they're also kind of hidden from view. None of my friends who are currently progressing through the MSQ know what Eureka or Bozja even is.