Ret is good in PvP. And while Ret is 12/14 in DPS, the percentage between 12th and 4th is a marginal amount. Unfortunately, Mage, Warlock, and Melee Hunter then blast out ahead of everyone else, skewing the chart.
Meanwhile, Holy Paladin is servicable in PvE, but a joke in PvP.
Prot is meh. Can do the job but other tanks are far ahead in mitigating damage. Obviously Prot is just a non-starter in PvP.