I understand you always put on a happy face and defend the current status quo, however heroic 50th percentile is laughable and defending the current situation is even funnier. Which percentile and difficulty we use IS relevant because in heroic, the adds absolutely melt. They are a snipe fest. Its AOE burst and a matter of who can AoE first wins. Mythic adds will be much more suited to our AoE. To further that, Mythic is where this damage is going to matter. AoE is our meal ticket for mythic and if we arent bringing home the bread there id say its very relevant.
https://www.warcraftlogs.com/statistics/7#boss=1692
Mythic 50th. Third, behind classes that are much better in other areas of damage. Mythic any percentile and we arent the best in our niche.
As I said. A niche is fine. If our design is to be dominant on AoE, than we need to be DOMINANT on AoE. We are simply not.
To further the point, if other classes are close behind, then we need to be close behind in other areas such as cleave and single target.
On the link I just posted, We have Warrior and Warlocks beating us with Mage, Rogue Paladin and Death Knights all right on our asses. Those classes just below us, absolutely dominate us in other aspects of the game and those above us do so as well. We perform terribly on cleave so when an instance is catered to our weaknesses, our strengths need to really shine when they are presented to us. We do not shine.
Its fine to have a "niche tax" but it needs to apply across the board and we need to be THE BEST in said field.