For the soldier battles that aren't forced, you can also choose to run away, although that will have a negative impact on your SeeD rank.

Tornado and Quake are two other spells that are very useful at that point in the game. You can get 20 Tornados from one Windmill, which you can refine from an Abyss Worm card. Quakes can be refined from Dino Bones (also 20 from 1), which can be refined from Armadodo cards (1 from 1) or T-Rexaur cards (1 from 2).