I agree that it would be illogical for the Idea Of Evil to be killed by Guts and Skull Knight, but I thought the Idea Of Evil was part of the World Spiral Tree.
You’re right Kenshi. Tenshinhan stated himself the eye lasers Gero shot at Piccolo were fast, implying they were faster than the ones he shot at Goku and Tenshinhan.
At the same time though, it encourages Guts to sacrifice the Black Swordsman Party. That’s definitely far more evil than taking revenge on Griffith and the Godhand, especially after they built Falconia, although it’s debatable whether or not it’s truly a paradise.