According to a 2018 Riot blog, it is true that based on, and I quote, "ALL THE DATA WE HAVE", the game outcome should be 50 +/-1%.
So I want you to think about that. Slowly.
What would "all the data" include? Just the player's MMR? Hahaha, very funny.
Quit believing that a huge game company like Riot, which has endured years of criticism against its matchmaker, would refrain itself enough to limit the matchmaker to "just MMR". Pull your head out of the sand. They have a lot more data than that, and don't fool yourself.
ALL THE DATA would include each player's average grades.
ALL THE DATA would include each player's behavior patterns.
ALL THE DATA would include each player's frequent picks, bans, hard counters.
Don't believe me? Search the following blog post for the text "all the data", to see the quote for yourself:
> Within the actual systems, most teams have an expected win rate of 50 +/-1%. This means from **all the data we have**, we think we’ve made a fair match.
So you should expect that if you score high win rates, the system will put the lower grading players on your team, and the higher grading players on the enemy team, to help ensure that the probable outcome is 50 +/-1%.
And you should expect that if you have good picks, the matchmaker will put you against enemies who will ban your pick, steal your pick, or hard counter your strategy. It's not bad luck. Riot knows you like that pick. You are aggressive early? Riot knows. It'll match you with opponents who typically ban your pick. Steal your pick. Opponents who better handle your early aggression. It's not bad luck. The matchmaker is actively working to oppose you, because your win rate went above 50%.
But why? Well, in the end, a 50% win rate already exists. Because for every time someone wins, someone else has to lose. However, Riot wants to "redistribute" the LP wealth, by stealing from the rich and giving to the poor. Think Robin Hood. Think Socialism. This redistribution would make it more difficult for anyone to "get rich", aka rank up. All this is so that high elo would be rare, so top players would be renown, and everyone else would wish to be like them. This dream of fame and stardom would make the game more alluring, more attractive, and more addictive.
I mean, did you really think that Riot went through all that trouble to create such a complex grading system, just so that you can see your S+ score at the end of the game? Haha. No. They created the grading system because they knew that MMR alone wasn't enough. Too many smurfs. Too many veteran players with years of experience. MMR alone couldn't quickly identify these players, but a complex grading system could.
So the better you play, the harder your games will get, even within the same elo. If you really want to win, you need to expect this to happen.
Only way to rank up is to play a diverse pool of champs, and change strategies frequently, so that the matchmaker can't predict what you will do. And then to play so good, that the matchmaker cannot find sufficiently bad allies, or good enough of opponents within the same MMR range, to stop you from winning.