We are advanced class. I expect, that when one plays advanced class, he is better than the one playing basic class. But only when he does things correctly. When he does them incorrectly, he is worse than one playing basic class. As simple as that.
So when you feel you are OP, it might be you reached mastery in playing this class. So, you SHOULD be better than 99% of server population in what you are doing.
But not everyone reached mastery. I bet less than 10% of capped wardens reached it. For the remaining 90% things like slightly OP DC is to be or not to be. Without it no one will take them ever into instance.
I saw many bad guards hardly tanking BfE t1, or tanking 6 men instances without greater difficulties. With good heals they were able to do their job.
I saw also many wardens who refuse to do group content, or do it only as dps, becasue they can't tank it. And i saw only few wardens on my server tanking willingly.
It means something.
For me it means that after wardens' nerf 1% of wardens' population will tank instances. The rest will grind hytbold dailies.