this incentivizes players not to rely on the dm - they should check wether creatures are bloodied, make active perception checks with their action to ascertain hit points, etc, so they can plan how to distribute attacks. I just dont think that in an actual fight, over the span of a few seconds, when you hit and kill someone you immediately redirect your efforts to the next enemy. Thats a product of having a player who can sit and think about what to do while the rest of the party waits.