No, you can have a brawler. The archetype is perfectly fine.
The point is that in the end, your tanks must be balanced in terms of contributed raid DPS, survivability, and enmity sufficiency. How they reach that end is where the flavor exists.
So you can have a WAR deal the most individual damage to fit the brawler archetype. The problem is you cannot also give them the most raid DPS support, too.
PLD is also fine as a "defensive tank." But, the problem is you cannot also give them the least raid DPS support or else you have the current imbalance.
It's about balancing raid DPS output IF the meta is centered around raid DPS.
I'm not saying this is the solution, but going on the previous example of Storm's Eye's damage contribution, if you removed Eye from WAR and gave it to PLD, assuming that PLDs do 10% less damage than either WAR or DRK, then the result is 3 tanks that deal the same damage regardless of their pairing (excluding double pairings). But, two of the tanks deal more individual damage to fit their fantasy while one does less damage but makes up for it through raid DPS support.
Back in 2.X, PLDs did more individual damage than WARs when in Sword Oath. But, when you factored in Storm's Eye, WAR DPS contribution was balanced. Now, PLDs do less individual damage AND they have no raid DPS support.
