Europeans don't really run suicide Karthus nor do they see it as a strategy from what I've seen. They treat Karthus' passive like Anivia's; it's a second chance in case they make a mistake, not an excuse to go super aggro.
Also pro players dont sit in Karthus ult when he goes in suicide. They exhuast him and kill him and then move back and fight 4on5.
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Realo won gold at the Sex Olympics with a BROKEN FRIGGIN NECK.-Voltch