This is entirely wrong.
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“On fire” has nothing to do with the ranking system, at all.
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The matchmaker always trys to find people with as close MMR as possible. There’s no “give this player higher MMR opponents”.
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The matchmaker isn’t some general artificial intelligence, capable of reasoning. It’s an MMR system. Your estimated “skill” is your MMR. If the matchmaker thinks you’ve improved, that means your MMR has gone up. Those are equivalent statements. Everything the matchmaker gleans about how good you are is wrapped up in your MMR, one number that goes up when you win and down when you lose.
Stopped spreading these ridiculous myths. Once again, Kawumba has taken a lot of time to detail how the matchmaker works, including ample citations to actual posts/comments/etc from official blizzard employees. Read it instead of falling for “fake news”.