2c as I'm not really a tank main nor theorycrafter for tanks, but I think the main issue with PLD isn't that it's bad at much (other than single-target damage) mechanically...

But there's something to be said for the fact that 90% of the time you're a one-combo job with an AOE button, some Off-GCDs, and a bundle of defensive cooldowns that aren't very exciting or interactive to use (compare timing Sentinel with managing Wrath/Infuriate/et al to get Inner Beast out in response to an incoming Big Attack, etc.)