there is a simple way to rework that gem.
Just look at Krysbin’s Sentence. I think this is how this gem was originaly meant.
You deal (old scaling bonus/2) increased damage against slowed enemies.
lvl25: You gain a slowing aura and you deal 2,5 times this bonus against enemies afflicted by any other type of control-impairing effect.
But there are already long topics on legendary gem rework ideas
