PLD can still tank...
Only reason why WAR does it better is because it does a CRAP TON more damage than PLD. Add Vengeance and Antagonize and WAR just incurs more enmity. Therefore WAR can hold hate while DD's can do MUCH more damage. Its simple really. When I first started doing Cutter's Cry with a PLD tank we were fine till last phase of Chimera. PLD couldn't hold the damage output that the BLM's were doing much less the heals needed to keep the PLD alive. We switched to WAR and BOOM we got our first kill. I wonder why that is... WAR has more enmity generation due to Steel Cyclone being on a low recast, Rampage healing them and not to mention Antagonize and Vengeance. Just popping Vengeance alone at the start insures you start off strong as hell. With enough enmity to keep the mob on you through the first barrage of cures and nukes.
Now let's fast forward...assuming you know how to play PLD (because I assure you most people dont, including myself) and now you have some enmity gear (by enmity I mean more than just a +10 off your belt) you can now produce a lot more enmity through your sub par enmity generating abilities and possibly be able to hold off the blms and mnks. Since you have more damage mitigation than a WAR you are now tanking better than a WAR could ever dream of. Dump your HP gear PLD's and stack the enmity you might see a difference. This is all speculation and my own personal view of the PLD vs WAR debate. I could be wrong.