I think I'm rank 1 platinum right now but I have a 75% win rate. So I'm playing at mid/high diamond level but I just haven't got promoted yet because I only have like 30 games played.
If your win rate is 60% or above then you are likely playing at a higher level than you are currently placed and with more games it will even out till your win percentage gets very close to 50%.
I'm in a bunch of diamond ranked teams though. So many people I know have the game that I rarely get the chance to 1v1 ladder because people are always hitting me up for team games and they are so much fun. lol