I'll field this one, since I have both pld and war at 75.
I think the answer you're looking for is that war can tank most mobs decently, but pld and nin just do it so much better.
Keeping in mind, of course, that the following explanations are for endgame type mobs. Bigger stuff, if you will.
Over the years pld has been handed a pile of new abilities and modifications to make it really shine as a first class tank, and in the right hands are certainly not mp sinks. How so, you ask? PLD/NIN. Before you go lulzpldwithoutprovoke, we've since seen (and some have conducted themselves) testing that shows that the Volatile Enmity (VE, or hate that decays over time) generated by Provoke decays at a rate that by the time 30 seconds have passed, all Enmity generated by Provoke has disappeared. The way pld/nin handles the loss of provoke (and it's not much of a loss to start with) is by mitigating far more damage with Utsu than they would ever generate with provoke, thereby sustaining Cumulative Enmity, the kind that you lose when you take a shot to the face.
Ninja handles hate building in a similar manner, by slowly building up a vast amount of CE by subbing drk and spamming blind, stun, sleep, and other spells. With the amount of refresh that can be given to them (spell, ballad, Evokers Roll, etc) they for the most part have little issue with mp and mitigate damage through shadows, like pld.
Warrior can tank decently, we mitigate our damage in the same manner as the above two jobs, and we hold hate through our damage. As we all know, war can and will tank at times whether we want to or not. Sometimes though, that damage just isn't enough, and we don't have the slew of abilities that pld has, nor the option of subbing a hate building sub AND keeping shadows, our greatest survival tool.
Hope that clears a few things up!