The PvP gear for tanks provides the same crit rating and comparable DPS that is equallized between all sets. The only difference is the higher protection.
The main thing that you see changing the dps of tanks in a big way are PvE accessories and weapons. Take away the Ibis, Sceptor of Return, or Manical Harm and Faction/T3/T4 rings and neck, you'll see a huge reduction in damage.
There might be some class balancing things for sure, but let's see how people preform after unchained goes live. Without PvE gear being available perhaps the PvP weapons will finally be worth something.