Currently? " SAM/BLM/MCH " are the only true Selfish-DPS Jobs.

Your idealistic FFXIV as far as I can understand...
  • All Melee DPS become selfish DPS
  • All Raid-Buffs are shoved onto BRD/DNC/AST
The problems you're creating would be...
  • Rebalancing Issues of Melee DPS
  • Forcefully Nerfing BRD/DNC/AST personal DPS
  • Meta would be completely ruined
  • Every Job that loses a Raid-Buff is easier to play
  • Possibly harder to play BRD/DNC/AST? And a lot less rewarding
  • Loss of Chain-Stratagem requires adjustment for SCH

These changes should fix something
Yet I have no clue what it solves... Square obviously spreads out responsibilities to not be purely on x Jobs. Think mitigation and shielding is not all on the Tank nor healing all on Healers, they give bits and pieces to other jobs and Raid-Buffs is no different. This creates team-work, but also makes it less likely to blame x Job or 1 person for everything of a specific responsibility since its most likely spread.

Lastly? You're potentially going to piss off a lot of BRD/DNC/AST mains that will be forcefully nerfed from Personal DPS due to drastically buffing their Raid-Buff utility. Specially if it's Raid related? when a good majority of those players don't care for Raiding at all.