Miser's Mistress is a good example of a melee-DPS battle. However one of the reasons that is possible is the lack of aoe damage she deals. Thus WAR is still a better tank since it can DPS very well on her. PLD's talents are lost on that fight.

You can probably imagine if there was a melee-dps preferable fight where those melees did take damage, that it would likely be off-set by curaga spam or some other whm-induced mechanic/spell rather than the addition of a PLD. They could go hand-in-hand surely, but chances are the responsibility to keep the party alive would fall more in part on the healers than the tank.