It didn't used to proc per kill. It used to proc per DAMAGE. Which is why it was broken. Now it procs once like it's supposed to, and has a timer before it can be used a second time to prevent abuse. You might as well say Plan-C is broken because you can't keep swapping back and forth constantly activating the effect. You can now activate it once per grenade, which is what it was intended to do from the beginning.