That also punishes someone who is placed at the end of a strike. They could do a percentage type thing however, like someone mentioned, there are some people paired in strikes that don't have as good of weapons as others. Usually I take a big chunk of strike kills because I have the icebreaker, VOC, and a bunch of other exotics and good legendary weapons. Some of the people I have been paired with only have rare weapons still and a percentage system would punish them.