Also dude, Yaulthoon is a uniquely difficult fight, using the hardest fight anywhere close to that level range as an example is fudging it a little bit don't you think? How about the rest of the chain? Or any of the 100 other quests within 5 levels in either direction? You're underleveled, on the highest difficulty, and if you're attempting yaulthoon, I guarantee you're blowing through everything else. Yet you're using all that as evidence that there isn't a problem? You've just made my point perfectly. Fix the difficulties, just a little. I'd be happy with a modest health increase and a corresponding xp per min increase.
Also the games diversity is not reflected in its dungeon system. in heroic there's only one difficulty that gets used. It's a problem, I promise.