Let me start this discussion with my first skill "upgrade", which I noticed didn't seem to be much of an upgrade at all. That is Kneebreak. It uses the same timer as kick, and cost more power. When I watched how much damage I was getting out of each one, I saw no difference. Hence, I have no reason to use kneebreak.
The second skill I noticed that didn't appear to be any type of upgrade is Ruin. Now, it says it does slashing damage over time, however I have only noticed a single hit from Ruin. It uses the same timer as Mangle, and does less damage. Again, I see no point of using this skill.
So someone tell me, am I missing something, or are these skill "upgrades" in fact not upgrades at all?