dragonfire dive doesn't suck, plumes are simply magic resistant. blm is useless for them, monk with FoF is useless for them, dragoon 15min is useless for them- as i've already said.
monk is far superior to dragoon in single target dps. dragoon has great (but not amazing) single target dps, and makes up for any shortcomings there with their aoe capabilities. in fact, played correctly a dragoon has some of the best aoe of any physical dps job in the game- rivaling warrior with their OP steel cyclone (while having much higher single-target dps than war). all things being equal, dragoon will almost never match monk in single-target dps. therefore you bring them along for good single target and great aoe. period.
so, yes. you do rely on dragoon to aoe. but you don't ask dragoon to handle *all* of the aoe. that was never the point and never implied. all physical dps with aoe contribute to burning down plumes. (and again- monk is exempt from this if you have enough physical dps that you don't need them to game FoF)
stating a preference of how things "should be" is one thing, but what i've said is simply the reality of current job design.