Powerful weapons? You forget that FF has weapons so powerful they are simply called Weapon; if you're pooling together everything in the games then as well as the heroes you have Sephiroth, Sin, Emerald & Ruby Weapons, all versions of Omega Weapon, Yiazmat, all summons, GFs and aeons, the dark aeons and Penance (!). And if you're saying all of the UNSC etc then FF has Shinra's army, all SEEDS, the combined armies of Alexandria & Lindblum, the Archadian battle fleet (you talk of powerful vehicles in Halo, let's not forget the sky fortress Bahamut, Dreadnoughts and Light Cruisers) and its accompanying Imperial army. And all those could be used as cannon fodder while the heroes, villains, Weapons and summons launch a full on assault on wherever Halo's commanders are. In short FF would slaughter Halo.