K:D is a pretty shitty way to balance classes. If every class has the killing potential of a two-hander or a polearm user, then you don't have balance. There is such a thing as risk vs. reward. Truth is, archers stand back and let everyone else take the risks. You can play a "riskier" game by staying closer to melee, but you're still low risk comparatively. Same with 1h vs two-handers/polearms you have a forcefield, thus less risk.
To go further still, as it's important for people to realize this with ranged; Archers hit the same enemy most, just before a melee clash. This means that over the span of the 10 seconds or so that it takes an enemy to go from max accuracy firing range to melee(not with the archer, but with his team's melee), as long as you don't land the killing blow (which would most likely require 3-5 hits depending on armor), chances are you won't get the killing blow as the guy you were focusing on, is now lost in the initial melee confrontation. Even if you did 1/2-99% of his HP, you still didn't get the killing blow, thus you just scored a lower amount of kills than what you (in one way or another) deserve. And this is every single round and for each melee confrontation within the round, that this happens.
At the end of the day it comes down to this: Kills are determined not by those who do the most damage, but by those who get lucky and land the killing blow. I'd love to see the average amount of damage done per round for each class. I'd bet that archers get twice as much damage, at least, than what the average amount of hp is, yet still get half as many killing blows. Whereas melee is probably closer to a 1:1 3:2 ratio.