From us messing around in dungeons with pld and war it is easy to see the difference.

Pld takes a significant amount less dmg per hit and has the ability to heal themselves (generating hate and lowering the stress on healers), but deals alot less as well. Enmity generation is much higher then on war with equivalent gear.

The thing with Pld is the lower dmg output, in a game with so many speed elements the only way to make pld a valid tank is if the DDs are having to hold back with a war tank. In this case the dds could increase dmg to be overall more effective then using a War. A good pld should allow dds to up their dmg by 15% easily across the board... if that is the case the over all dmg increase across the party from using pld is > the loss dmg using War. Issue is if the DDs are going full out and cannot increase dmg from a war to a pld... the lost dmg will not be made up.

Honestly Pld is a much much better tank, but you have to be able to cover the lower dmg output in a speedrun setting.