i always thought that it should encourage team play more. Sure you get stacks for champion takedowns, but not enough. It's less risky and typically you spike faster if you just afk farm creeps; but, i agree it's pretty misguided to incentivize NOT being a team player. seems contrary to what a lot of this game is about.
that said, I've definitely become a more cautious and overall better/safer laner because of this thing. If i see shyv,udyr,yi,nocturne (FUCK), etc. , i just assume it's fend for yourself lanes. basically a 4v5 until ~20 min.
anyway, my suggestion would be adding stacks (50?) yet tweaking the power either along the way or once it's sated. Make the spike more gradual basically. And, of course, 1 stack per large monster, 2 crab / 5 dragon is ok i guess, but 2 stacks per champion kill/assist to promote more team play. idk