Doing damage is extremely overrated. Putting a target down so that he can't fight back is much more valuable to a team.
Imagine two people fighting one guy. They are both trying to kill him. The first guy manages to hit him 3 times, the other guy gets the last hit. Should he be rewarded more, just because his hit happened to be the last hit? Same intention, does way less damage, but gets lucky and gets the last hit. Bra-fucking-vo!
Dealing damage is something you should be rewarded for, cause it is something you control. Whether it is the last hit or the hit before the last hit is not something you control, so you should not be rewarded for it. People are killhungry enough anyway, and the e-peen on the scoreboard is enough reason to kill for everyone apparently.
The scoring system is a joke. Proximity needs to be removed. Why should some guy get points for just being close to someone who is doing well?
Oh I don't know, maybe because the downblock you've been holding is the only reason why your teammate manages to kill him with a sideswing. Presence close to an enemy is a huge distraction to him and a huge part of teamfighting is helping your teammate getting the hit. Damn shame if I should stop effectively teamplaying because only kills get rewarded.
Often I see people with zero kills at the top of the scoreboard.
So? If anything kills are overrated. The new system is a lot better at showing who is actually valuable to the team compared to the kills list. It's just ranged that get very little points.