Several posts point towards the fact that PLD need some time to build hate before DDs could actually join in the fun.
There could be a very small improvement to fix this issue.
Flash should be modified to give A LOT more Enmity if used on a non-agressive enemy.
This way, if PLD engage with Flash, they will have a very nice boost on enmity and DD could start the fight just after without worrying about enmity. Of course, in the long term, PLD still have to manage his enmity/MP/Cooldown if he wants to stay at the top.
Besides, GLA would also benefit from it, for people who prefer tanking with it.