ForceStealer
Double Growth
I dunno, Sephiroth sure didn't seem to want to deal with the Weapons in VII. And I don't know if Omega Weapon counts as a "character," so they're probably less concerned with his power relative to Sephy. but I honestly don't know if AC Seph could defeat Omega. Given his penchant for controlling a large chunk of the corrupted Lifestream, it's very possible, but I don't know.
But I HIGHLY doubt Cloud could just run swinging his sword and hope to beat Omega. The entire team couldn't even beat Diamond, only deter it from advancing further. It was Chaos that possessed the necessary power to neutralize it. Yes, of course things are contrived such that the main character of a game will be able to kill a threat, but if anyone other than Vincent could have done anything to Omega, I'm sure they would have. Vincent told Cloud he'd handle the Tsviets.
But I HIGHLY doubt Cloud could just run swinging his sword and hope to beat Omega. The entire team couldn't even beat Diamond, only deter it from advancing further. It was Chaos that possessed the necessary power to neutralize it. Yes, of course things are contrived such that the main character of a game will be able to kill a threat, but if anyone other than Vincent could have done anything to Omega, I'm sure they would have. Vincent told Cloud he'd handle the Tsviets.