I was going to say that if KH3 Sora fights Phantom, he would be too powerful for that boss, but you mentioned it. Still-oh! I thought of something cool! There should be a battle where you can fight all the bosses at the same time, and you can bring Donald and Goofy, or you One versus everyone, or all your allies from previous games can join in the fight, or if they bring Kairi, Lea, Roxas, Xion, Namine maybe, Aqua, Ventus, and Terra in the group, it can be all the Keyblade wielders vs all bosses. It would be the best optional fight in history that would take a long-ass-time. Excuse the language. I hope the PS4 can be able to do that, because that's a Villains vs. Heroes. Still, just imagine someone trying to do that mode on Critical, that would be insane! Also...one of many of the strong optional boss fights....Sephiroth. Adding Sephiroth and Lingering Will with the rest of the bosses, One vs all is too much for Sora, but I bet someone in the world can do it. Sorry for the fanboying, your idea was too good not to add my own.
I feel you. Rewind would actually show how strong sora has grown.