I figured that the developers wanted to establish Cid as a non-combatant for storyline purposes.

Several characters that hardly appear in a battle have completely working sprite sheets. Gestahl, Kefka, and Leo can function as a playable character in the party without any issue.

I wonder why they didn't have Cid appear in a battle scene like that? Maybe he is too old to fight? But, you can argue that Gestahl was just as old, yet he had the power of magic...