Games where handicaps and spreads are used, ergo proven useful since they would have long been abandoned if they weren't, are simply this:
If shitty player comes within X points of winning, it counts. This is implemented by either adding X points to the lame player's score, or allowing wagers on a bad team at least keeping it close.
Since damage modification affects the rate of points being earned, not actually how the score is tallied, you are going to turn it into Everyone Gets To Be Equally Okay no matter how you handle it. And, a simple point handicap won't matter either because people will say "well, I really won, it's just giving him a five-frag ass-pat because he can't compete on my level."
"highest kill streak" = Camp.
Here, pretend I had posted one of the many scoreboard screenshots I have of me getting dozens-long killing streaks on cradle. I don't have that HD plugged in right now because I don't game anymore.
It also means that if one guy gets, let's say, a 20, and the clock is run beyond half-time, why bother to play the rest of the round, when you know you just don't have time to compete with the current frontrunner? That's the shit that made original The Living Daylights suck shit and sent it to my drawing board.