I agree,Skarner should focus on being helpful and a bit tanky, not in 1v1 duels. This runes may be useful for dueling or killing, but Skarner should go for another rune path in order to be more helpful and have a better focus on fed champions at team fights.
It´s just my opinion

There is two builds here Child devourer is actually the one I use most of the time the assassin thing was more of a thing to try out use either one but child devourer is the one thats meant to be showcased here.