In
this thread there's a suggestion for using Carbuncle as main pet and changing all Summoner's job skills except for Fester into single-effect summons of each Primal, thus allowing for much more gameplay variety and making the job feel like a true Summoner.
Here are some examples (they're all off-GCD skills and each one prevents you from casting another summon for 5sec after use):
Ifrit: single target attack with a potency of 110 and 2sec Stun effect, 30sec cooldown;
Titan: reduce the damage taken by the user and the pet by 20% for 15sec, 120sec cooldown;
Garuda: aoe attack to the target and the enemies nearby it with a potency of 90, 30sec cooldown;
Leviathan: delivers an attack with a potency of 30 every time the user or the pet get hit for 20sec, 120sec cooldown;
Moggle Mog XII: refresh MP with a potency of 80 for 20sec (similar to WHM's Shroud of Saints, it's an easy fix to MP issues), 180sec cooldown;
Ramuh: single target attack with a potency of 140 which spreads and hits nearby enemies with a potency of 70, 90sec cooldown;
Shiva: aoe attack with a potency of 30 and a 20sec Bind effect (this would actually substitute Tri-disaster), 30sec cooldown;
Odin: instantly kills the target (works only on trash mobs, misses on others), 300sec cooldown.
P.S: The potencies and durations are just there to give a general idea, they would probably need to be adjusted and balanced according to the other jobs and skills.