I see alot of people complaining about ranked lately and I think a large part of the problem comes from ranked matchmaking being mmr based.
The thing with mmr is that nobody but riot uses it and when looking at a player skill level we look at his elo not mmr since mmr is hidden from us so people normaly want to gain elo not mmr but this is where the problems start : lets say you're at a plat level of skills and you play ranked and get placed silver 5. So you probably are going to stomp and carry most games and your mmr will rise alot but after a few games even though you are still silver you'll notice you are being matched with plat players that are at the same skill level as you but hey they are plat and you are silver so you are expected to beat plats to get out of silver wich is absurd and it just keeps people from getting to their right rating and start climbing. Now in the usual case people are not that far from their right ratings but it is here where the problem really shows specialy with low elo players I see alot of people in bronze 2/1 getting matched with silver 3/4 after winning a few games wich is stupid. for a bronze 2 to get to bronze 1 he should be able to beat bronze 2 players not silver 3/4 and in my opinion he should not be matched even with bronze 1 unless in promos.
I understand that the mmr system maybe effective against smurfs but there are other ways to handle smurfs like increasing the lp gain cap so that the people stomping most their games can get out of their devision in 2 or 3 games and make them skip devisions.
Another problem I've seen lately is people getting worst team mates as they go on winning streaks , again the mmr system is the problem : if you are winning alot of games your mmr will increase and when looking for a game the matchmaking will do one if 2 things :
1/ look for a teams around your devision with similar average mmr and because you have an mmr better than you devision's you will get team mates worst than your devisins skill level to even out the average mmr wich means you probably are better than all the players in the game but your team mates are worst than all of the 5 enemy team players.
2/ match you with players higher than your devision wich brings us back to the first problem of beating higher elo players to get out of a lower elo
So in my opinion the ranked matchmaking will be better off placing people with players of the same devision while mmr should only be used to determine how much lp a player gets and if he should or should not skip devisions.