I've posted the full details in the tank balance thread, but even exclusively focusing in on the upper percentiles, it's about a 200+ dps difference between WAR and DRK for most fights except for V2S (V2S is actually pretty close for all three tanks). That's about the same difference that you saw in 4.01 between PLD and WAR, when players were clamouring for PLD nerfs and WAR buffs, so I don't think that it's pocket change. At least, it wasn't a few weeks ago, before the re-balancing that took place in 4.05.
Stance usage is inversely proportionate to percentile, and dps uptime is directly proportionate to percentile. Your personal dps directly influences clear time. All these things are incorporated into your overall performance. You can come up with any number of excuses why you aren't performing as you could ("I sprained my forehead on the Fell Cleave button"), but generally speaking, when you're looking at a variety of different players in different setups doing the same fights, they become a pretty good representation of tank performance.
Personally, I'm not interested in pure potency buffs. I think the majority of DRK's issues come from the resource penalties associated with tanking and using our mitigation moves, and addressing this will go a long way in unlocking the job's versatility. It doesn't need to be the highest dps tank. It's actually extremely fun and engaging to play.
In HW, we were theoretically supposed to do less damage than WAR (by virtue of their superior design, of course), but there were still plenty of DRKs out there who managed to outperform the average WAR (not that the bar was all that high to begin with). It comes down to those points you mentioned: minimising tank stance use, maximising uptime. I'm fairly confident that we'll continue to find ways to do so irrespective of more punishing job mechanics, especially when the majority of the WAR playerbase doesn't understand the value of uptime tools like Onslaught. You just have to strive to be 20 percentiles better.
Everyone struggles with different things. I'm simply pointing out that if you're struggling to outperform a PLD/DRK comp on WAR, the data shows that it isn't the job that's holding you back.