Super push won't always guarantee a kill. If you launch someone with super push/repulse you need to take three things into account: 1.) Are they hitting a flat surface or a sloped surface? 2.) Is the object that they're going to hit close by or far away? 3.) Are you close or far away from your opponent when you super push/repulse them?
If there's a good distance between the object you've launched your opponent at, there's a moderate distance between you and your opponent when you launch them, and the object happens to be sloped or your victim hits the object at an angle, you'll deal virtually no damage to them.