Obviously there's been a lot of hot discussion about this topic, so I'd like to further add more discussion to it.
One thing I've realized recently is that I no longer look at jobs based on their current sub-roles: melee, physical ranged or caster. I now only look at jobs based on Selfish DPS, Moderate Support, or Heavy Support. This is all I think about when considering how much aDPS a job should do, given I believe all jobs should be within 1% of each other in total rDPS.
So looking at each job as to what they currently bring for raid damage buffs:
Selfish DPS: BLM > SAM > MCH
These are the guys who should be top 3 aDPS above all others. The only time I consider things such as job difficulty or mobility is when comparing it to these others in their "new" sub role. I don't compare MCH to other physical ranged, I compare MCH to other selfish DPS jobs. I think BLM is less mobile and higher skill cap than SAM, and SAM is higher than MCH given MCH's mobility, so I think this is how it should be.
Moderate Support: MNK > RPR > SMN > DRG > NIN
These are the guys that bring some raid damage, but not as heavy as others. Thus they're the middle of the pack. It just so happens most of these jobs are melee, though I would not be opposed to seeing DRG and NIN drop to heavy buffer if their raid buffs were equivalently improved, as I think that fits their job identity personally. I also think it would be neat if all of SMN's summons had support auras like Phoenix does and turn them more into a BRD-esque caster, but that's a whole other can of worms of a topic lol.
Heavy Support: RDM > BRD > DNC
These are the guys that don't do much aDPS but bring tons of raid damage buffs. Sadly, RDM's Embolden doesn't really do that enough currently so probably needs to be addressed. This brings me to my next major point.
I do not believe that defensive/healing/raising utility and mitigation on DPS jobs should affect their aDPS. This is important because rDPS should be within 1% of all jobs. I do not believe in Raise, Vercure, Tactician or Addle/Feint taxes. Leave these types of taxes to the tanks since tanks have no raid damage buffs (and I don't believe ever should).
So now we come across to how this could affect party composition. I believe the standard SE wants most parties to be is 2 tanks, 2 healers, 2 melee, 1 physical ranged and 1 caster. While that sounds great on paper, we run into problems like MCH were they may have decent aDPS but their rDPS is so terrible compared to all other jobs that they are just not valued for their ranged slot compared to any other job, much less BRDs or DNCs. This was only further compiled against them with P8s' fight design heavily favoring melee uptime and having such a strict DPS check.
How would party compositions change if we looked strictly at raid damage buffs instead of the classic "melee/physical ranged/caster" that seem to define each job's damage?