Well, Sephiroth's got power scaling going for him. His limits can be described as 'better then the 2nd best people in his world'
2nd Best include guys like Chaos Vincent, Omega Wiess, Minerva, WEAPONS in general, and so on.
So you've got a guy with the Speed of Chaos Vincent and Omega Weiss (But more), the strength of WEAPONS (but more), the magic of Minerva (but more), and so on.
He could've jumped into the middle of Omega Wiess vs. Chaos Vincent and kicked both of their asses. Though at that point, he'd probably have to actually be trying. He might even break a sweat for once.
Once you power scale him properly based on the best of his world, you see that Sephiroth's fight with Cloud was actually Sephiroth halfassing it so much he might as well have one hand behind his back and be blindfolded for all that he's really not worried about Cloud.