Match making is terrible because the ranking system is terrible. Nothing will ever make it better unless you fix the poor ranking system, changing the mmr you see, changing the names of the ranks its all meaningless window dressing that does nothing. The match making is terrible because the system is terrible so you have people in insert x rank who do not belong there.
1) we are on the same team but we do not equally contribute to every match wins and losses. We should not share the same reward and penalties. There are plenty of metrics that demonstrate this and you can easily create a fair system that augments the gains and loses for each teammate based on thier contribution. No I am not advocating you get 0 gains because you went 0/10/0 I am saying if you go 0/10/0 you shouldnt get as much as the player who went 20/3/5 and vice versa for how much you lose.
No I am not saying you only look at KDA, you weight in CS, KDA, total dmg delt to champions, kill participation, gold generated and anything else that seems like a reasonable metric to determine your personal performance and contribution to the match outcome, and you weight it in proportion to your opposing role. Compare ADC to ADC support to support.
After all of that if you fall outside a set percentage of your counter part on the enemy team you are either granted a bigger share or lesser share of the team MRR/LP gains/losses for that match.
2) all new accounts start at the very bottom of the ladder and have to work their way up no more sticking people i the middle and ruining the middle of the ladder eternally. Yes I know alt smurfs will stomp irons hint they already do... and they stomp silver and golds too you cant change that unless you get serious about policing alt accounts and riot will never do that, but atleast this way the non smurfs dont also mess up the middle of the ladder as well. The smurfs will rise fast and hit their proper elo just like they do now.
3) Get serious about addressing the exploits to rank, account sharing, duo q etc... yes I just said make a true solo q ladder...there are plenty of modes to play with your friends there is zero real reason for duo q/solo q mix beyond exploiting the advantages duo q provides and its the worlds easiest way to boost people.
Now you will end up with people playing at their proper ranks and you will get much more competitive matches, you most likely will reduce toxicity as well, because why? Well if I decide to troll most likely I will simply impose larger penalties to my own rank instead of everyone elses. You gonna put and afk farm top because you got ganked 3 times? Ok its fine yes we will still lose but you will most likely lose 4x what the rest of your team lost, such that you are only penalizing yourself finally and after a while you will learn to suck it up and do your best , got filled to support? Ya sorry happens to us all better do your best or again eat 4x the mmr loss....Gonna rage and AFK? enjjoy the 5x lp loss. Gonna rage and int? Agian you will end up with 5x lp loss. Know your intenret is awful tonight but continue playing with 1000k pings? Yes enjoy the string of 5x LP losses.
Only real solution is to give each player their own lp losses and gains based on their performance other wise nothing will ever fix the horrible match making in ranked.