The two reason imo that Pld is inferior to War is.

1. Max HP is lower.
2. Damage output is much lower.

When it comes to low man content when you can get away with a WAR tank people will use it because it does more damage and results in quicker runs/speed runs. However, when there is 20+ man content in 2.0 I think you will see Pld tanking the majority of that content. Though atm WAR is a better tank because of its base max hp, and if they gave PLD a good increased in max hp they will be much much better when that 20+ man content comes. I do not believe a 10% dmg reduction is necessary or even remotely balanced.