Sion and Karthus shouldn't win prize fight in their passive

In order for their passive to activate, they need to DIE FIRST.

Prize fight clearly says "take the enemies' lives before they take yours".

In both cases, you take their life first. They simply reanimate after death and take yours back.

It's wrong that they win prize fight in their passives. You won the fight. They simply got some revenge.

Adding this point: If you get first blood for activating their passive, you should win the prize fight. It's inconsistent with how they've been treated since they were made.