Generally, your rank improves by MVP's and won rounds.
If you always win 16 - 0, you are not loosing points at all and only win points. A won round against certain ranks compared to your rank gives you a certain amount of points, loosing against them compared to your rank looses you a certain amount of points.
MVP's give you extra points, which if playing against higher ranked enemies would boost your rank alot.
That doesn't mean that you can always plant the bomb and win by bomb explosion and not killing the last enemy since VALVe changed the way to determine who get's the MVP. If a player got a tripple kill in a round, it might happen that he get's the MPV even though the round is won by bomb explosion.