What Vengeance was supposed to be
To quote Ghostcrawler, "Vengeance was designed for a single purpose, which is to make sure tank threat scales as other players improve their gear." That is, while DPS classes are accumulating DPS stats that increase their own threat and tanks are accumulating survivability stats with absolutely no threat benefit, tanks can still keep up with the raid DPS's threat potential by "converting" part of their survivability into threat.
And yet, at the same time, "A tank shouldn't be able to just auto-attack and let Vengeance do the rest. Vengeance isn't a replacement for the tank generating enough initial threat to get the targets to stick to her."
So when first laid out on paper, the story was this: Threat was still going to matter, and Vengeance wasn't there to make the pull any easier, just keep that shadow priest off your ass at the halfway mark. Fair enough. The devil, however, is ever in the details.
Here's where it all broke down
First and foremost, the implementation of free damage for tanks lead to tank damage being left behind. While in Ghostcrawler's initial case of Vengeance, he tossed out the hypothetical number of a tank doing 50% of the damage an actual DPS would do with Vengeance up. The reality, though, is that we're not always rocking a full stack of Vengeance. In Dragon Soul, tanks without Vengeance stacks are reliably doing about 25% the damage output of a DPS player (about 10-12k DPS, using Theck's numbers), a piddling fraction of the numbers a damage-dealer can dish out. And this introduces a host of issues.
And the Light help you if you have an avoidance streak at the start of the fight. Have fun wildly throwing out taunts to keep that mage from being eaten.
Moreover, how about the pitiable job of the off tank? Unless they're an endangered CatBearTank, what chance do they have to contribute anything to the total damage of the raid when Vengeance dictates that their damage output be anything but flaccid while the current tank gets all the Vengeance stacks, in addition to all the glory?
Then, finally, when the off tank's time has come and they get to taunt, they find themselves in the unenviable position of needing to out-threat a juggernaut with maximum Vengeance without losing aggro. In some cases, the previous tank may be forced to either stop attacking the boss or to use a macro to clear off his or her Vengeance stacks.
And in addition to that, think of the poor play that Vengeance incentivizes, from standing in fire to build stacks (something I always did on Alysrazor while waiting for my egg to hatch) to inconsistent taunt swaps to keep each tank's stacks up (all the while confusing the hell out of the healers).
Finally, in terms of scaling, consider what happens when you go back to old content in your shiny T13 tank gear. Have you done a heroic lately in that gear? How far did your Vengeance stack with all your accumulated avoidance and mitigation stats? As Theck says, "Does a DPS spec generate 50% less DPS as soon as they set foot into an instance they out-gear? Of course not. So why should we?"
What could be
It doesn't have to be this way. The biggest problem with Vengeance's implementation is that it is dependent on the tank's actually taking damage. As detailed above, using that premise as the foundation of the formula creates all sorts of problems, from reverse scaling, to avoidance making our threat weaker, to incentivizing bad play, to neutering the off tank.
The solution that Theck proposes is Vengeance to morph from a reactive, stacking bonus to something entirely different. In his design, Vengeance would give you a 50% damage bonus to NPCs and scale with the tank's stamina value. This would turn Vengeance into something that steadily increases, regardless of the content being tanked, with the additional knob to turn of how much stamina exactly offers in scaling. It's genius in its simplicity.
Ultimately, having read Theck's post, I hope his conclusion has had the same effect on you, dear reader, as it has had on me. There is something rotten in Denmark with regards to Vengeance, and not just with regards to the look and feel of tanking. Something more intrinsic and foundational. And it cries out for repair.
The Light and How to Swing It shows paladin tanks how to take on the dark times brought by Cataclysm. Try out our four tips for upping your combat table coverage, find out how to increase threat without sacrificing survivability, and learn how to manage the latest version of Holy Shield.