If Paladin is "specialized in defense" shouldn't its defense be better always?

[Adrasteia]

PLD has Hallowed, and 99% of enemies have physical attacks that you have a chance to block. There's no huge difference in mitigating tankbusters.

There's a huge difference, considering the prevalence of Magic-based tankbusters. The difference between healing a DRK MT in A4 and a PLD MT in A4 is pretty well night-and-day, speaking from personal experience. I'd gladly toss Hallowed Ground in the garbage if it meant I could get 30% Magic DR every minute.