Why not? Isn't it shown several times throughout the FF VIII franchise that Cloud himself bests Sephiroth [At the very end of FF VII between Cloud and Sephiroth, Cloud and Sephiroth in FF:AC, Cloud and Sephiroth in Dissidia, etc.]? It would seem to me that if Cloud utterly defeats him time and time again, then it should be obvious that he's the stronger of the two.