Besides the ranking system being broken, there are other issues in how the system is manipulated.
First, although I have not seen this myself, one friend has reported being offered gold to lose a game so the other person could advance. In the same way, people can play against friends (or other personal accounts) to increase their scores by having the "competitor" lose.
Second, people have admitted to me that they stop playing at a certain point because their score is high enough. Stopping on the peak prevents others from competing and gaining correct ranks. Good players with multiple accounts can then use another account to try to obtain another peak. The same tools (your brain) should not gain additional wins.
Make the ranking system work so players are encouraged not to manipulate the game. These are forms of exploitation.