I'm a relatively new player, so I'm first going to acknowledge it's going to look like there's a lot more content to me than it would for someone who's been playing a lot longer. However, ignoring the existing content, it seems to me like they're still updating things at a pretty decent pace. New raids are coming soon as well as the deep dungeon system. They just released some more of the story, which while short was pretty compelling for being outside of an expansion. Along with that we also got a new trial (with ex as well), a 24-man raid, and a hard mode dungeon. Maybe it's because I'm coming from SWTOR; now that's a game that is truly dying from lack of content and a woefully understaffed development team. Coming here was a huge breath of fresh air, where the devs seem to care and the game gets substantial updates in a regular period of time.

I'm not trying to say that your concerns can't be valid, but perhaps your expectations are a bit too high, if not potentially impossible. No game can produce content such that it will satiate people who spend all their time in the game. It's unsustainable. Unless of course we want the game to move into a much bigger grind, which would I'm sure scare away all but the most hardcore.

I think in cases of burnout like this it's important to move onto something else for a while or try to mix in other games. For me, if I have some down time in a game, if there's not a lot to do I'll start playing something else as well. I like a lot of different games so I have a whole big back log of games that I want to get to eventually. In fact, from a certain point of view sometimes it seems like MMOs have too much content because it keeps me from having time to go through all the other games I want to play. And that's a good problem to have I think.