Flare isn't your only problem: you'll get rolled by his lightning spells too. Shellga takes priority over Protectga, I'd say, but both are useful because the creepers do a lot of physical damage.
I didn't even see a single lightning spell on my first try. Too busy getting Flares in the face. With this knowledge and the fact the dogs are vulnerable to Sleep...
... Bahamut SIN "Cid Mission" complete!
Cait Sith is amazing.
Also Rift Gilgamesh was a hilarious fight to Cid Mission, much less Master the damn thing when the run started pretty poorly as well. FFV is probably my strongest realm, but I didn't expect to get by not bringing a breakdown to go with Full Break, nor with Bartz dying so early in the fight (he got one Tornado Strike off before Enkindu blasted his face).
Galuf was the hero here, with his Fist of the Dawn and Unyielding Fist.