It's not to match the DMR, but to give less skilled players a chance to get some shots in. See, in Halo 3, skilled players could have less skilled players down in a couple of seconds. No time to adequately react. It also requires more skill this way to get a faster kill. That way, newbs can get some shots in and some xp for helping out rather than shot down the whole time. In Halo 3, if I was shot first, I died. In Reach, i had a chance due to the 5 shot.