FF6's final dungeon has you using 12 party members and yeah this can be a problem for people who only used the same 4 for the most part. Cause you want at least 6 strong characters by that point.
If you have all 14 characters, you end up having to leave two of them behind. What two did other people leave on the airship? IIRC I'd always leave some combination of Setzer, Relm, Locke, and Umaro. I think Setzer was generally who I regarded as the worst character, not sure if I knew about Fixed Dice. At this point I think Relm is really good at spells, so I guess I'd probably leave Locke and Umaro. Umaro being un-controllable is a big detriment. But now that I think about it, one of the three statues uses ice attacks heavily (Doom/Demon?) so having Umaro in whatever group that is, with the Snow Muffler equipped, would make him worth it.
Tough call who to leave behind in this game.