At this stage the rankings should be thrown out, after all it doesn't mean or stand for anything. Academy students being able to take out hunter nins, is a prime example of just that. The ranking system is complete decoration. The hard work that people do to kill Orochimaru is being belittled, while you can just simply stay at level 15 and gain the same amount of strength (if not more) and not have to go through the hassles.
On top of that, if you are a good ninja and stay at level 15 forever, you might be able to actually battle people many, many dks ahead of you that are working hard at getting DKs. So you get rewarded twice: 1) You can get unlimited attack and defense points, and 2) The flood gates of potential people to attack becomes even wider.