I think that’s kinda closer in comparison, but it’s still not there. Slaughter stacks super quickly with very little skill required.
Uncanny is also close to requiring weakspot hits, but that’s also easier to stack since weakspot hits are comparatively easier to hit than ranged weakspot… and it only needs hits not kills. Pinning fire on the other hand just needs you to hit stuff… Ghost has a very different bonus but that one requires just hits.
It’s like combining the requirements of Slaughterer and Ghost into one with a ramping damage boost. The boost is also useless if you are one-tapping anyway and feels bad if you don’t… Although you can then just rely on the stacking while standing still thing… Which roots you in place which is also bad.
Sorry for the rambling, I really like you mentioned this, didn’t even think about this angle. Kinda fleshes out my problem with it.