Why is MMR like this?

(Numbers are totally made up, so don't read too far into them. Apologies in advance, this is wordy.)

Just want to start here and clear this up before answering the original question. While you do have separate ratings when you play either Killer or Survivor, MMR for the two roles are definitely connected. A 1500 rating Killer would be matched with a 1500 rating Survivor. Each role is somewhere along the same sliding scale, they aren't scored in completely different ways. Beyond that, the win/loss conditions for each role are the same (but flipped, of course) - and this is a very crucial part which I'll get into next.

For a rating system like this to work, you absolutely need one winner and one loser or a draw/void. In order for one person to gain MMR, another person has to lose MMR. This rule, combined with the way your rating changes more or less depending on the rating of the people you faced, prevents ratings from climbing endlessly and becoming meaningless. The best player in the world will eventually run out of equal or better players to beat and stop climbing once they've reached the top.

This is crucial. If both players can win at the same time, their ratings will both increase even though their actual skill level stays pretty much the same. They could then face off again, and despite being at the same skill level as before, gain MMR again. Across millions of matches, people would generally trend upwards.

To put it a simply as possible, you go from the follow possible outcomes to a match:

• A win
• A loss
• A draw/void

To these:

• A win
• A close match that also counts as a win
• A loss
• A draw/void

There are more opportunities to gain MMR than to lose MMR. Your MMR becomes more of a reflection of playtime than actual performance. An average player could climb to 2000 MMR by playing a lot and end up facing a really good player who happens to play much less often. If that happens, the system has failed.

Now applying that to hooks like you've used as an example, say the Killer hooks each Survivor twice and all Survivors escape.

• Every Survivor gains a lot of MMR because everyone escaped
• The Killer gains some MMR because they got most of their hooks

This is that exact situation where both sides gain MMR simultaneously, breaking the entire system. The only way to fix it is to draw a line and determine who won and who lost. Does the Killer deserve the win because they got 8 hooks? If so, is that fair to call it a loss for the Survivors who not only escaped, but kept all their teammates alive? It is incredibly muddy and impossible to say for certain who deserves to move up.

This is one of the reasons why MMR is based on kills & escapes. For one side to win, the other side needs to lose.

Beyond that, they act as a "proxy" for skill - in other words, playing really well will usually result in you catching and killing more Survivors, and vice versa. The reason why we use a proxy is because it is impossible to accurately assess someone's skill with a formula. There will always be a what-if that throws a wrench in things. "What if it's based on hooks? But what if the survivor escapes in the end anyway? But what if it's based on chase times? But what if the killer is tunneling someone and I never get chased, so the best move for me was to do gens?" and so on.

To put it bluntly, it is impossible for any matchmaking system to accurately assess your skill from a single match. No matchmaking system in the world can do it. There will always be too many factors involved to say definitively, and so proxies are used to help gauge where you should be over the course of many matches.

All this is to say: Your invisible rating going up or down is not a reward or a punishment. It is not to make you feel good or bad about yourself or the match you just played. Its only purpose at the end of the day is to find you a roughly even match. If you're had a close match where survivors are hooked multiple times and one or two just barely escaped, this is a good thing! The goal in that case is not to raise your MMR anyway and give you tougher matches. You are already in a decent spot where the competition is close. You might gain a little here, lose a little there, but in the end you'll be hovering around that spot until your skill changes on average.

I completely understand that it feels good to have the game say, "Way to go, you did well!" in a scenario like that, but for it to increase your rating when you're already having close matches would be a failure on its part and only lead to more frustrating matches where you are outclassed. The only goal for the system is to keep you in that close match sweet spot where you're comfortable, nothing more.