PBSR is just a functionality of making it so that under 2900 SR gains and losses from match outcomes can be adjusted based on your performance. MMR is always free to move as much as is needed, including zero. Once you’re not a new account, and have been playing a sufficient number of games, the uncertainty metric of MMR lowers and MMR becomes more stable, therefore it moves less extremely, and more similarly to the SR.
There’s a section in the guide about the conflicting information from Scott Mercer’s posts and why Kaawumba interprets things to be what Jeff says, which was explicitly that “Only MMR is used for matchmaking”. PBSR is a change to a visible stat, whereas MMR is a secret stat. We don’t know how much it moves in a win or a loss, but we have been told that it adjusts more freely than the constraints that were placed on SR.
This is a title of a section that has a good amount of info on this.
This is not a thing. The match maker does not pre-arrange wins or losses for either team. Every match is created with the intent of being as close to a 50/50 win chance for each team as is possible within the time it takes to find the right people.
When he says “nearly guaranteed to win”, this is not talking about intentional actions on part of the matchmaker. The matchmaker is using skill information that is POTENTIALLY inaccurate. So, if your skill information is inaccurately low, then it will be accidentally putting you in matches that are easier than they should be. If you continue to lose those matches due to the reality of randomness and team synergy, then your MMR will get lower, and potentially be more incorrect. Eventually, if the MMR is wrong enough, then the games will get very easy, and the chances will increase that you’ll win. There is no such thing as “rigged to guarantee” anything. When MMR is inaccurate, then the chances are just slanted in the direction of correction, because your actual skill is different than their model of your skill. They’re putting you in matches that are INTENDED to be completely fair and even with the understanding that MMR is not a perfect model of skill, just the best that exists in the Overwatch ecosystem.
People talk of statistical probabilities, but others interpret those as intentions, or aims, or bad things. The matchmaker is not a person, it doesn’t seek to even the score. The matchmaker doesn’t care how many games you’ve won or lost, it just takes the MMR and tries to put you in a fair game based on that MMR and the MMR of the people queued at the same time as you.