So currently there are some issues where Pld isn't wanted because they do less dps AND take more magic damage than Drk. Everyone seems to also agree that if the fights had more physical damage Drk would likely be the one getting sat.
For this to work several adjustments to some jobs needs to be made... I am also aware of Drk having some other issues but that isn't important right nowAfter the changes I will explain the thought behind these changes.
Pld changes: Rage of Halone threat greatly increased and the duration of strength reduction reduced to 15 seconds.
Drk changes: Delirium int down moved to power slash and duration reduced to 15 seconds.
Mnk changes: Dragon kick int down effect removed. Blunt resistance changed to 5% and add 5% damage to all sources BUT does not stack with other abilities like this. In other words you can have monk 5% or the better 10% slashing from war/nin... you can have monk 5% or you can have 10% piercing...
So what does all this do?
Right now Pld has a threat problem and a dps problem. By increasing threat on Rage of Halone Pld would be batter equipped to use Royal authority. If they want to get the most out of mitigation on physical bosses they will have to limit Royal Authority use because of the str down effect being shorter. At the same time they wont care about that on magic bosses and can just go full dps.
Drk would be going through something similar. More damage on physical bosses because int down doesn't mater and lower damage on magic bosses because they need that int damage on the boss if they want full mitigation.
Monk not having int down prevents groups from just bringing a monk and a pld leaving the drk out. It also solves an issue monk has with group support. Extra support for everyone but not as good as if you had the class with the specific attack bonuses.
One other thing for this to work out no boss should ever have an AoE raid wipe mechanic that requires/nearly requires the str down of a pld or the int down of a drk.
The int/str down duration of 15 seconds would force pld/drk into no more than 1 dps rotation before going back to their main combo to get the debuff back up. It could be lowered more to restrict them to choosing between extra damage or keeping those debuffs up 100% of the time. It also may not have been clear but if done right on physical bosses these changes should leave pld being the best for damage taken and drk best for dps... and the alternate for magical bosses. Unless of course they don't care about those debuffs then both should be on similar ground with the extra threat pld would have on RoH.