The problem is people are inherently selfish, or there are enough who are, who do not care about other people or their experience and will put themselves first. Therefore there must be punitive action towards leaving or you see people leaving “90% of their games”.
I have no sympathy for you with these penalties considering I can confidently say I have not left 4 QP games early since OW2 came out let alone 4 of my last 20 or 20% of my games. The root cause of the issue is the natural human selfishness and there is no real cure for that.
If you are imaging that there will be some perfectly balanced game of QP then you are deluding yourself. It does not matter how accurate the MM is it will never happen because it cant happen because you cant know how serious someone is going to take said game of QP.