Riot Games kept the secrets of League of Legends matchmaking rating (MMR) tightly under wraps for years, but support team may have inadvertently spilled the beans by stating that win/loss ratio is only a secondary parameter in the formula.
Many League of Legends speculated that MMR is decided on factors other than win/loss ratio, but a recent exchange on Reddit may have shed some light on the MMR calculation formula. A League of Legends player by the name Blizz Grimmly sent a support ticket because their connection broke during a match, after which they promptly reconnected.
Blizz Grimmly then apparently proceeded to win the game while his teammates didn't have any verbal conflict due to the disconnect and neither did they report the player. Though the game was won, Blizz Grimmly lost League Points (LP), which is the transparent part of measurement that decides whether they go up or down on the leaderboards.
According to the support team, nothing could be done to restore the lost LP since the Leaver Buster system prevented the player from gaining any, but their MMR would be left untouched as the main measurement for such is how players perform during a match, which is indicated by the letter grade, with S+ being the highest they could obtain.
Some Redditors immediately dismissed the claims, stating that the support team tends to give out wrong information via ticket responses and no one would likely take the statement seriously if another Rioter didn't swoop in, claim the information was false, and the thread got locked by a moderator with an explanation that the title contained inaccurate information.
Now, the information SapMagic provided in the aforementioned reply states that MMR changes only happen based on each team's MMR ratings and the outcome of the game, be it a win or a loss.
SapMagic's info could have some merit as better grades would be incentive to pad the stats during a match, which is a process that could ruin teammates' experience. But then again, if grades indeed impacted MMR and under assumption that no one knew about the interaction, it could provide a more accurate matchmaking system.
That said, there are two questions that Riot Games didn't answer, and possibly dodged. First, why is Leaver Buster not up to the task, since it prevents players from gaining LP even though they reconnected and carried their team? Second, what did actually happen to Blizz Grimmly's MMR, since he won the game but lost LP as if their team was defeated and the support team's info was supposedly wrong?