Using GilToss is very useful against Neo-Exdeath because it will hit all of his parts for a lot of damage. I'd suggest making everyone a Freelancer or a Mimic for the final battle. If you're willing to do it, return to the world map and learn the Blue Magic spell Big Guard (use Control on a Stingray in the Waltz/Worus ocean area). Put everyone to the back row. If you have Ribbons, equip them (Freelancers can equip them).

Start the final battle by casting Big Guard, Golem and Haste2. If anyone dies or gets petrified, revive/heal them and cast Big Guard and Haste again. Have your White Mage heal and use Holy, have your Black Mage use Flare, have your summoner use Bahamut, use X-Fight if you have it, (even better if you can use it with Two Swords) and use GilToss. Keep recasting Golem every now and then.

When you're fighting Neo-Exdeath, try to attack all the parts at the same time. If only one part is remaining, it will devastate your party with Meteo, so GilToss and Bahamut are really useful here since they can damage all the parts. Good luck, because Exdeath is one of the more challenging end bosses in the series.