They're not even in the same column. Throwing knives are a melee ability with its own column. Shoulder Charge is an innate ability in the Passive Ability column. Same as Stalker, Shadestep, and Angel of Light. Yeah, they're not equal in their function, but they're all designed specifically for these Subclasses. I could maybe see them adding a passive ability to Gunslinger that allows Throwing Knives to explode after hitting a target, but not just simply making Throwing Knives one-hit.