You people are reading bits and parts of my guide, not the entire thing.
I'll say this once more.
The way I've played him and explained in this guide is to kill one or more people while sacraficing yourself for the better of the team. You may not get a bunch of kills and you may die a bunch, but when you bring the entire enemy team down to 50% with no kills and then your team Aces them easily after to clean up, allowing them to push a tower, then you did your job.
People can insult and point at whatever they like. This strategy works as I'm still rising in rank when I hardly know anyone above 1700 in these forums. The win percentage shows just how well it's been working as well, overall I made this to try and help people, so you can accept it and try to improve on Karthus play/Ranked games or you can not.