as a PLD main, I'll put it this way. I think it is much easier to be a "good" tank than it is to be a "good" dps. (never healed, sorry you fools don't get included =P )

What I mean is, if you are a halfway decent tank then you are forced to pay attention to many different things. You are watching emnity, you are watching your party members, you are watching enemy positioning and any nearby enemy patrols. You are controlling the battle, so you are forced to pay attention. If you aren't doing those things, well, you probably aren't a halfwar decent tank.