I like Garnet because I find her very useful in battle. But lately her summons do little damage.

Zidane physical attacks = 1000
Steiner physical attacks = 1200
Vivi magical attacks = 1100
Garnet summons = 200-300

I only have 1 or 2 stones for each summon (except Ramuh, which is 22) and I understand that summons do less damage than regular attacks because summons are directed to the entire enemy party, but the damage still shouldn't be this low. Can anyone give me any advice as to how I can increase Garnet's summon power, aside from gathering more stones?