Well, 2.1 showed one thing. That if one of the 3 new dungeons is a bit more challenging than the others, then it will be less used than the other, easier ones. 2.2 showed that if one dungeon takes less time to complete than the others, then it will get used more than the other 2.

So the difficulty and average completion time should be constant amongst the 3 to get balanced player usage out of them. But anything 3 or above difficulty has ended up the same way, reduced in difficulty in some way in later patches. Personally, for me, instead of just jacking up the difficulty, I would prefer to see more uniqueness and different elements in them, rather than the trash to boss, trash to boss, trash to final boss, finish.