It's a mentality and based on wether or not you're sticking with your team. If you bolt ahead, you're a runner. If you stick it out with the slow movers, you're a completionist. I'm with you. I sparrow up and hit the checkpoints too, when everyone else wants to do that. I assume that the higher kill count is attributed to hitting the first waves of checkpoint mobs first before others arrive on scene. Look at the devils lair. If you get in there early enough you can rocket and mop up a ton of kills before your 2 team mates... Same goes for summoning pits. Skip all the starting mobs, activate the door and start hitting the spawn doors of the main room. You'll definitely have more kills.