Why do people act like the only purpose karthus' ult has is to execute enemies
Regis used to use his ult to start of fights and chunk entire teams for 2k+ damage. Why do people think Edge of Nights will always be off cooldown when Karthus ult? at best maybe assassins rush it. If the enemy champions are saving it's edge of nights active to dick Karthus out of his ult instead of being destroyed from various other spells and they can actually get away with it, you either screwed up or karthus' team wasn't winning that fight anyway.
By the time anything other than an assassin finishes this item, lane phase will be over and the window of opportunity to pick off low hp enemies after a fight in lane will be past. I seriously doubt this time is going to impact Karthus much at all.
ult, they deserve to lose.