It would take a considerable boost in DPS for tanks to supplant DPS. Bard, the weakest DPS in the game for E12 currently averages 20.3k at 99% while Gunbreaker, the strongest tank, averages 13.5k. Keep in mind, Range are notoriously weaker than any other DPS role—much to the chagrin of many. With that in mind, we'll use Dragoon, the lowest non-Range DPS who sits at 21.5k
Therefore, you'd have to buff tank DPS by 45% or more for anyone to consider replacing a DPS. No one is asking for such an absurd increase, but 15-20% is fairly reasonable. Basically, I think it's more than fair tanks can surpass dead or bad DPS players.
One of the reasons I often stayed on Warrior for O11S. Holmgang didn't work for that mechanic, thus PF couldn't whine about it. Speaking off disengaging for no reason, I have noticed the devs repeatedly having tanks do that this expansion and I really hope they knock it off. There's nothing fun about spamming Tomahawk in the corner. At least we've found a way around Anti-Air compared to Twisters in E6S.