If you won, you would be the first that I have seen use Cloud, Barret, and Tifa.
I used Cloud, Barret, and Aerith. It helped me a lot because Barret is a tank and Aerith has a lot of MP.
Barret is great on Leviathan, just keep shooting him when he’s flying.
When I fought Bahamut, I kept using Barret for long range attacks and would switch often.
You really need to have barrier or manawall on for bahamut because he will use his super move and that’s it.
Make sure that you use revival earrings too and make sure you have them when you face bahamut.
Magnify and Barrier.
Barret is the truth IMO.