meh, same difference :p

they arn't based on kills, its damage done, which killing a lot of specimens does help, but can be obtained without any kills.

Is it just me, or does it seem like there would be more "secondary" things you should have to upgrade in order to level up perks? Medic has healing (primary, but it's not damage), support has welding, commando has stalker kills, and sharpshooter has headshot kills. yet we have 3 perks that rely on nothing except "kill lots of enemies."
Just a thought.