I've played my Jugg vengeance since I created him... shortly after this game launched. Either I'm messing something up horribly... or Immortal DPS is... a sad joke. Yes, you get great cooldowns. But you lose the same amount of HP because the fights are taking longer. (As I said - maybe I'm not doing it right?)
If I have the choice between regging after destroying an enemy in 20 seconds and regging after gnawing on him for 5 minutes... I take the 1st option. Not to mention that in pvp a good fokus helps the healer even more than a taunt or intercede. Well... about the same... but those two things can be done as vengeance, too.
Immortal isn't a DPS spec. It's a tanking spec. And if you aren't geared right then being in the Immortal tree won't help you a whole lot in terms of survivability. And yes the fights will take longer because it isn't a DPS spec. What the **** is regging? And while focusing (spelled with a "c") a target that's attacking a healer is helpful do not underestimate what taunts and intercede can do for a healer. But as a tank you should have the healer guarded in a warzone or an arena which is more helpful than either of those abilities and you have to be in the tank stance to use that ability.
Also, AoE taunts won't be useful to Vengeance Juggernauts in 2.7 as it will become a threat drop in anything but Soresu form.