neither of those things reflect performance?
Is there ranks or anything similar for winning games? I'm not sure how this works, I've just seen clips of matches on YouTube but looks and sounds greatYou gain mmr for a win and lose mmr for a defeat, but the amount you gain or lose is based on your personal score and the match score.
If you lose the match you will always lose mmr and if you win the match you will always gain mmr, but the amount you gain or lose depends on how hard you won/lost and your personal score.
Some examples (I'm going to presume each match is ft10 but that's an assumption):
Let's say I win 10 - 2 but my score is 3 kills 12 deaths and for that I gain 35 mmr. I'm still going to gain a significant amount of mmr because the match was won but not as much as a player with a good score would get. So, in the same match (won 10 - 2), a player that had 15 kills and 2 deaths might gain 55 mmr for that result.
Let's go to the other side, the team that lost 2 - 10. Someone on that team with -1 kills and 12 deaths will lose loads of mmr, let's say 60. Someone with a score like 15 kills and 12 deaths in that match might only lose 25 mmr.
None of those numbers are accurate because I don't have the exact formula but I hope it demonstrates the idea to you. Basically players who get good scores will gain more mmr for wins and lose less for defeats.
Here's a period of my match history on the Native version so you can see how that works. The mmr gain numbers are lower here than they currently are because the formula was changed, so numbers above 50 are more common in the current version: