i agree with most of what Xurts said. i doubt the amount of cells would changes sephiroths power. if sephiroth was concentrating and completely trying to beat him he would win. ive just realized that cloud never beat sephiroth before. in the flashback in FF7 cloud caught him off gaurd. in the north crater with bizzaro and safer sephiroth he had help and the final fight of the game was just a mental thing and never really happened and it was a representation of sephiroth (i think.) sephiroths overconfidence probably cost him the battle.