Dungeons are as rewarding as they can be. Any other rewards they add would be worthless in weeks as they get farmed out.

Trust me, if dungeons were completely unrewarding then they'd be dead content that you needed trusts for all the way through MSQ, but they're not because we still have people queueing into dungeons to level up, to farm for tomes or to get roulette rewards. That's... something. It's more than regular trials have(hence why there's excessive queue times for them at times).