KDR is the best example of skill. If you constantly play you will slowly move up the ranks regardless of your skill level as you continue to accumulate kills. However KDR shows consistently how you perform on average... so when it comes to rankings like the GameMe ones, yes KDR is the best example.

If you want to see who is actually good at this game, who understands it and the meaning of teamwork, then scrim.  There are tons of Pub Stars who cant scrim for crap because they have no understanding of teamwork or strategy(angles, adv points) and just run around gunning on pubs.