But the whole difference is in how these skills achieve their results, isn't it? In the last fight between Ahhnold and Venom Demon, Ahhnold dropped 3k Rampage with his first hit, reducing Venom Demon to some 15% health. And ultimately lost. Would that happen with KO?

Just to be clear, I had KO fighters in the past and I know very well that they don't score KOs in every fight, not even in every three fights. The problem with the skill is not in how often it triggers but what it does when it triggers. There is a imbalance between actual efficiency of the skill overall - which isn't anything exceptional and from that point of view the skill is OK - and the manner in which it helps you score wins - which just cancels the fight because of a "lucky" dice roll, leaving no chance for counter.