I believe the process for determining leaderboard ranking closely resembles this flow chart:

I don't know the exacts however:

It goes purely off wins. If you lose a match, it doesn't effect your ladder score. If you beat a player with higher ladder points, you gain more. Similarly if you beat someone with ladder points much lower than yours, you gain very little. The reason you see players with lower wins higher than others is because they've beaten these high priority targets more.