LOL, that thread is awesome. I mean, really guys? You could just watch a youtube video of the fight instead, following what the player is doing there, for yourself. Even a very mediocre player without much skill should be able to kill the Kayran with the proper strategy and preparation in reasonable time...
But I guess @Tommy must really like the Kayran fight given the fact how often he did it just for other people in this thread...
The problem isn't usually the player, but their PC. The QTE at the end just doesn't work correctly on some PC's, sometimes because it's close to minimum spec, sometimes because of certain drivers (some high-end keyboards). So no, nothing to do with player skill. They're playing exactly as shown in those videos, and it still doesn't work.