Sephiroth is superior than Ganondorf. He's a superior swordsman. We can see that Cloud is an offensive fighter when he battled Kadaj, Loz, and Yazoo and yet when he battled Sephiroth Cloud was struggling just to keep up and Cloud is an excellent swordsman.
Sephiroth is much faster than Ganondorf, we see Sephiroth capable on cutting the top of an entire building in half as it collapsed (because of Sephiroth), and Sephiroth was capable on cutting through large columns with ease as he battled Cloud.