I think AoE threat is like single target with the WAR. The ability to have buffs effect overpower, and the ability for overpower to crit is what pushes it so far ahead. You can even slot Flash if you're that worried about your resources to ease the cost. Although, you know very well that this really isn't necessary. The combination of overpower and SC means there's no need to actually flash anything if your resources are stressed, you can just stand there and refresh TP and still have a threat lead. Not to mention, overpower also isn't all that expensive if you've got a little time to recover after its use. If you're talking about using it in the middle of a long boss fight with few breaks, you may need to be careful about your TP, but otherwise it's not going to be an issue.
And there is a benefit to having it be TP based. For groups where you get a little break in between, TP restores much faster than MP. WAR has the advantage if you split groups up at all and don't pull everything. The PLD needs to spam riot combo if they empty their MP pool, or they won't have enough MP for the next group. On the WAR, even if you completely empty your TP, you'll probably have it back to half full by the time you get to the next group. And even if I find that I really need to conserve, it's usually just fine to switch to single target skills and throw out the occasional SC when wrath is full.
Anyhow, I *finally* got my PLD to 50 and it's really been night and day. I find the WAR's resources & threat much easier to manage in AoE situations due to the ability to be able to pull so far ahead up front and the faster speed at which TP is restored in between pulls. Oh, and you're doing a ton of damage as the WAR, so you kill stuff faster too.
I'm not saying that PLD needs the same AoE killing power and threat gen as the WAR, but there should be more parity.