The other tanks contribute DPS but neither has the self sustain of a PLD so they still need healer care. Including properly executed holy stunning, a PLD can survive even the largest pulls for 30+ seconds without needing a single heal. Try asking your healer to not heal you for 30+ seconds as a WAR or DRK and see how that goes for you. They can give you their answer while resurrecting you.
Based on the few situations where you're gated out of larger pulls, I lob to pull, Sheltron, Flash once on the gather, FoF, CoS, FB, Swipe, and RB on the primary target and then GB on either the second / third / fourth target. Lob + Flash + a FoF buffed CoS, FB, Swipe, and RB is more than enough enmity to hold your primary target unless you are under geared. Flash + a FoF buffed CoS + GB is more than enough to hold over moderate AoE DPS. If you have a summoner in the party you might need to be a bit more careful about your overall GCD budgeting and possibly flash again.
By the time they make their way to kill the second, third, and fourth targets, GB's DoT will have had plenty of time to tick. On 4+ targets PLD does start to fall behind but the difference is still not that large.
And like I said in my original post, I'm not saying PLD doesn't need some help. I'm saying just adding DPS to Flash so it's basically Unleash / Overpower is not a smart change because it only helps in very limited situations. Flash will still be completely useless in the large majority of situations. PLD already has enough situational garbage in their kit. They don't need more.
I'm not saying this is a good change but for example, if they added a 10% resistance down (probably way too high) that didn't stack with other effects like Storm's Eye, Disembowel, Dragon Kick, Trick Attack, or Foes then they'd buff the overall AoE DPS of a PLD party considerably and turn Flash into a staple skill that is usable in every situation.