While more DD is always welcome, as other posters have stated, PLD's enmity generation is not the problem.
I think a new "Provoke" -type ability would solve most of the issues, but instead of generating enmity for the user, this ability would:
1. Lower the enmity of everyone on the target monster's hate list (excluding the ability user). Enmity -30% on a 90 secs recast seems reasonable to me.
2. Additionally this ability would also decreases enmity generation for everyone taking action towards target monster (again, excluding the ability user.). This effect would last 90 seconds and decay over time from enmity generation-80% to enmity generation-20%.