Far better and simple SBMM system
Instead of trying to capture the nuance of what skill is in both survivors and killers, there is a very simple way of measuring skill/effectiveness in each match. Each player, survivor and killer, can get either 0, 1, 2, 3, 4, or 5 points that's awarded at the end of the match and your mmr rating would just be a running average of that 0-5 number (or you can make it 0-50, 0-500, etc if it's easier for the numbers/averages that way).
For survivor after the match is over, each teammate (aside from those who dc) who participated in that match get the number of gens completed in that match (0-5) factored into their average mmr. This makes it so that efficient teams that consistently finish more gens, will have a higher mmr and therefore be matched accordingly with other efficient players and against killers who can handle more efficient teams. And then of course teammates that urban evade around the edge of the map would more consistently not compete as many gens and would get matched with survivors who similarly don't and against killers who need those less efficient teams to help them get kills. This system would make it so that you don't get punished if the killer decides to just facecamp you out of the game or if you loop the killer all game only to die after all the gens are done. If you're at all part of a team that's contributing to the completion of gens, then your mmr will go up.
For killer, since the objective is to kill survivors and there are many different nuanced ways of accomplishing that task and many different killer powers and scenarios that could cause you to try and get kills with more or less hook states, you would just have the killers mmr based off of how many survivors they kill. You wouldn't want to base it off generators repaired or anything because there are some killers or builds that play for an end-game play or just get stronger as the game goes on but can still achieve the same end result. So obviously it would be a running average of 0-5 still for killer, 0-4 being based off of how many survivors were sacrificed in that match, and then the 5th point could be awarded if the killer gets a 4k without exit gates powered/5 gens completed or maybe with a certain number of hook states, etc. Whichever way, the 5th point would be an indicator that you not only 4k'd, but you did it with an extra amount of skill.
In this system every player gets matched as close as possible to each other that way efficient survivors are more likely to get matched with other efficient survivors and also against killers who are more skilled and better equipped to handled a more efficient team. On the other side, killers who typically struggle a bit more to get kills will start getting paired up against survivors who are less efficient on gens and give them a bit more wiggle room.