my suggestion for fixing kalista
It seems like the major issue with kalista is how impossible it is to chase her. Why not remove the aspect of her passive that increases her jump distance if she goes backwards? Is it really necessary to have her be literally impossible to catch without a dash in order to preserve her kit's flavor?
Also, I agree with everyone else that popping her stacks should be capped against neutral monsters. The cap should be at least 25% less than smite at any given level.