The problem here is Passage of Arms. People are going to argue that it's not a real cooldown because it's a dps loss when active, but it's also a potential 18 second personal Rampart coupled with an extra raid-wide mitigation skill over all other tanks. This is vaguely reminiscent of the "Inner Beast makes WAR the most defensively robust tank in prog", coupled with "Inner Beast doesn't exist in farm/speedruns, so WAR is at a defensive disadvantage" argument from previous expansions. If you want to address the issue, you have to change how PoA works.

To be fair, GNB has it worse. Camo doesn't come close in value to PoA.