Complexity doesn't have to equal difficulty in the encounter. I'm sorry you've found a bad healer but that's not what I mean when I say complexity.

What about a randomly generated puzzle you have to solve in some dungeons? However that may look, it would keep people engaged.

Or perhaps a free roaming dungeon in which you have to kill certain monsters to get through to the end/boss.

Or even better, why not make it feel like the End of Days actually happened across Etheryis? IT happens in two zones in the entirety of the story, and we "fix" the problem by telling people to stop thinking nihilistically.