Matchmaking does not have much influence on how snowball matches are. Yes, a mismatched game is always really 1 sided. But if gameplay is snowball even 0 mismatched games.... are still going to be snowball. At the moment the behaviors that really show up in my games as highly negative are far more related to players then MMR.
MMR is objective and wont give a shit about in game experience. That's not its job and there is a very small amount of impact you can make with MM adjustments that are not better fixed by targeted behavior systems.
At the moment, to many folks are rushing damage and often ignoring a balanced team comp. Players tilt and give up at the drop of a hat. 1 lane loses and folks check out mentally when then makes your team down 2 players (or more) because 1 did poorly... and realistically all 5 of your teammates being superior to their counterparts is a game your expected to win and a mismatched. If its "All of us are better then the enemy so we won" that's not a surprise and not at all a good indicator of personal skill.
Im grinding a new account and the losses I have tend to be directly related to teammate behaviors far more then any mismatches in skill. Last loss, My mid flamed jungle because he did not invade with her. Then flames top for not following lane. End result of that game is top never left lane or made any effort to play. Enemy on 2nd tower? csing top. Enemy on Hibi? Splitting top. Enemy on nexus? Still splitting top. All because mid demanded he roamed or followed lane in a way that his response was "Fk you. I don't leave lane this game now."
The jungle started shit talking mid and refused to help or gank their lane or group with that. So now The Adc and I are stuck in a match with 3 deadweights.
Not surprising, it was 1 sided and we lost. All due to behaviors Players made not from any kind of skill gap in a mechanical/micro/macro issue. You don't have good odds unless its grossly mismatched, 2v3 2v4 no assistance defending objectives. You just get more deaths trying to make a play compared to the folks running around clearing waves and camps. Then once they start rotating to pick off mindless farming champions the gold gaps just get wider and wider.
Frustrating, but I blame the players who did that not the MM.