It isn't. While kills and deaths are the easiest way to show your usefulness, there are a myriad of other ways that one can help the team. High strength builds will yield a better K/D, but that doesn't mean that you're not just as useful when you're dancing behind your team mate with a pike, ready to swoop in to poke the enemy while he's busy fighting someone else. The same goes for the many archers that stun a skilled tin can when he would otherwise make quick work of whatever poor sods he's facing.
And what about those naked guys with 10 athletics that run endlessly, getting half the enemy team to chase them? It's not as obvious to the unobservant in battle, but even a dullard can see that in siege, his efforts are invaluable to the team.
Here's a simple scenario: a smaller team with a surplus in support players has Goretooth. They follow him around, and he gets almost all the kills- the smaller team wins. Next round, he gets balanced to the other side and the smaller team receives Strongulator. The same thing happens again, except Goretooth is on the losing team and Strongulator is on the winning one.
It's nigh impossible to fight against a team with a few skilled heavy hitters and lots of good support. It's just a question of whether you're in it for the glory or not. If you killed ten people by yourself and your team loses because it lacks proper support, are you happy?
Poll