I know this is off topic, but why do you call that a mistake? Do you think that WAR > MRD in PvP? I had a huge conversation about comparing the Job and its Class in another thread, arguing as a proponent to WAR, but, after doing a bunch of the math and better understanding the mechanics of the class and its skills, I have determined that I was wrong and that MRD is superior in nearly every way. The only thing that WAR was shown to be better at was self-survivability. MRD seems to be a far better damage AND support class than the WAR job is, due to the cross-class skill selection, which makes it play the general role that tanks play in PvP better than even WAR does.
Given all that, I'm just curious as to what your reasons are for believing that WAR >= MRD.
Anyway, on topic: OP, I play a PLD in Frontlines and I love it. We actually do have a fair lot of damage, but it's found almost solely in our 4 off-GCD damage abilities (2 of which are PvP), Mercy Stroke (MRD), and Rage of Halone while pumped up with Fight or Flight. If I'm adamant on taking someone out, generally a healer, I'll try to hit them enough to remove any damage absorbs (such as Stoneskin), get them to around 80% health (most won't heal when at that amount), apply Fracture (MRD), and build up to where I can use Rage of Halone. Then, I'll pop Fight or Flight followed by Full Swing for the extra damage, use Rage of Halone, using Circle of Scorn and Spirits Within during the GCD wait, then using Shield Bash, using Full Swing during that GCD wait, then using two more back-to-back Shield Bashes. Generally, the enemy healer will drop low enough for a Mercy Stroke, and I can finish them off with a simple Fast Blade or, if they ran, 1-2 Shield Lobs.
While I do have STR accessories, I only have an ilvl 70 weapon, and this still works nearly every time.
Beyond my minimal, though existent capacity for dealing damage, I also chain CC amazingly. I can completely lock someone out of action while they're being focused for a full 7 seconds, 8 if they're a caster. Often times, all I have to do to ensure a kill on a healer is spam stuns on it the moment 1-2 other people are on him. And, of course, I minimize incoming damage to my team by CCing the enemy players who seem to be dishing the most damage.
I also love using Cover. Cover can be a real game changer. I have saved innumerable healers with Cover and Testudo (not at the same time, except in extreme cases since Cover doesn't stop magic damage). And, of course, I've managed to save healers by using Stone Skin on them and letting them get off a last-second heal while it held.
There are a lot of reasons to love my PLD in PvP. I enjoy it. I don't think the low damage is really holding me back from enjoying myself overly much.