Decouple the summons from the pet system entirely. It sucks trying to target a particular mob for AoE and having to wait for Carbuncle to transform and/or meander over there at low levels, meanwhile your target gets killed or the tank has re-positioned the pack and you only hit 1 target.

Then make Carbuncle 'useful' by having him do a party-wide spell that deals thorns damage when the boss uses a magic raidwide, similar to the Reflect skill he has in every other Final Fantasy. The Summon Carbuncle button can remain a pet for people who want their companion squirrel.