Right now i've been noticing that Skill > Gear > Class
That being said I've seen far more skilled WARs than PLDs and I've seen far more skilled MNKs than DRGs
I have a group I almost always play with. Myself on MNK and I have a DRG buddy who recently hit 50. Neither of us are geared incredibly well (both rocking AF for the moment) and he also has PLD.
Using Dues ex Machina as a comparison: when he went PLD he could not keep hate off my MNK. When he went DRG he could consistently pull hate when he wanted to.
I believe DRG/MNK are comparible, and it really depends on the skill of the player. I am far more familiar with MNK than he with DRG so my damage is slightly better right now as i'm more effecient with my combos.
But looking at PLD vs WAR I see one major problem that has various side effects. Damage = hate right now. You cannot get around this. the more damage you are doing on either class the more enmity you generate.
But being a tank you must balance enmity generation with survivibility. great defense is useless if you don't keep hate. and you're no good to the group dead.
Looking at PLD and WAR, both need STR for damage. WAR needs VIT as a secondary (plays a big role in defense, effects HP and damage floor) and PLD needs MND (plays no role in defense). and i know the role of VIT is minor compared to dLVL, but it still has an effect.
a WAR can essentially stack STR/VIT and go for defense/HP and be well geared to tank anything. VIT also adds HP so they will naturally have better survivibility. throw some +enmity /acc and you're a BAMF WAR.
PLD, on the other hand, must gear STR/MND for damage. but must also look at trying to fit VIT/HP/Defense and in some cases DEX for shield blocks. enmity is not needed as much due to the modifiers from MND on abilities. but PLD sorely lacks acc and must try to balance far more stats to stay viable. all of the really good PLD I've seen have capped stats and very effecient use of abilities and go for damage over defense.
I personally think PLDs primary stats should be VIT and PIE, not STR/MND. WAR i believe is fine as STR/VIT but PLD takes a serious hit when it gets no damage from a defensive stat like WAR does. if SE wants PLD to be the defacto tank than either the formulas need to change or PLD needs a major boost to its abilities. I personally think it's easier to switch it to VIT/PIE. However this may become extremely problematic in PvP, as this would make PLD monstrous. PLD could switch to STR/PIE and make it more of a magical tank and WAR a more physical tank. but then DRG would need to switch to STR/??? so there is no overlap.
TL;DR: WAR only needs to focus on primary stat caps and some secondary tanking stats. PLD has to balance primary stat caps against defense stats. PLD is more difficult to gear, so a PLD's skill level must be far greater to compare to an equally geared WAR to edge up.