A) Actually, you only need 1 WAR and at least 1 WHM and 1 puller to mass kill things in Abyssea.

B) While I would love for more AoE damaging BPs, I don't think that it will be used all that much. For what purpose did people use Thunderspark? Was it for the AoE ability to produce Thunder element damage, or was it for the strong paralyze, stronger than most other sources of paralyze?

C) Every summon already has a damaging AoE move, you mentioned it yourself, it is just that since BPs produce the same quality of damage upon single mobs at a lower price (both in recast timer and MP usage), people have forgotten the real purpose of Astral Flow. Mind you, it is incredibly cheap for the type of damage it produces.

All in all, I think what we have is just fine. Making the level 91-99 BPs AoE enabled will limit their usage severely because of gaining extra monster's attention to the party, even though most monsters will just depop or deaggro after the avatar dies. Only on certain monsters (Darters for example) will it cause a full wipe.