Confusion happens because the only things we show are CSR and SR. Neither of these are used for matchmaking. We use MMR. We’ve actually run tests to look at CSR and SR and both are significantly worse than MMR for the purposes matchmaking. However, they are also both better than MMR for Ranking and Progression respectively.
I'm having a hard time understanding why CSR works better for ranking than MMR. If MMR is what our matchmaking is based on why isn't displaying everyone's MMR numbers more accurate or better for ranking than displaying a different ranking system that hides the MMR?
MMR can run way ahead of what you've actually accomplished. It's a forward looking prediction at how we *think* you can perform, but not what you've actually done yet.
We can think way ahead of time that someone is probably Onyx, but then they go and completely prove us wrong by playing the next 20 games like a Platinum player.
MMR is also not a single number that shows your skill, it's a distribution. It's a complete bell curve. The middle of the bell curve is our best guess at how you're going to perform in your next game, so that's where we match make you.
But your actual Rank could be anywhere along that bell curve with some probability, so rather than assume you immediately deserve the middle of that MMR curve as your Rank, we make you prove us right first.
According to the math around that bell curve (normal distribution) your actual Rank has a 50% chance of being lower than we thought it was, and a 50% chance of being higher. So we don't want to just give you that Rank.
We want more data to prove our guess is right.
Another way to think about it if you are familiar with NCAA type stuff. MMR is, e.g., the BCS Ranking and CSR is the trophy / winning the bowl.