For the most part, I'd say this isn't bad in principle. Nor is vengeance the absolute worst thing in principle, though I still think there should be a reachable cap with Stamina becoming a DPS stat. But when it comes to actual numbers, I don't think Blizzard thought the mechanic through.
---------- Post added 2013-06-28 at 10:45 AM ----------
Meanwhile the other tank has 0 vengeance, can't actually be able to hold anything (because even after taunting, with a 200% threat modifier, that avenger's shield is going to instantaneously yank the mob right back from that poor no-DPS-stat warrior). Then you have tanks that chain-taunt on purpose to have more adds for more vengeance.
Obviously this is good for the group, but as for the other tank... well, when one tank is having fun, usually no one else is.
Overscaled vengeance, in all honesty, encourages pretty bad behavior in pug/LFR groups. I can say I wouldn't be so eager to disregard my group if I wasn't basically doing more than double the damage of the DPS and if pulling more mobs than intended resulted in un-healable (for average LFR-geared healers, anyway) damage.