If it’s being rigged(again, hypothetical, because we have no proof for OR against it), it’s not for or against anyone. The matchmaker isn’t trying to keep people down(or up). Rather, it’s trying to slow mobility to keep people playing longer. Blizzard doesn’t care if you’re in silver, diamond, or GM. They care if you’re keeping their game alive(and buying lootboxes).
This would be accomplished by offsetting your trends with players on opposing ones to make a game as even as possible. This results in as close to a 50-50 game as possible, whether or not you’re at your real SR. If you’re wondering how this is rigging, I go into more depth here:
Again, I’m not claiming this is absolutely the case, simply posing a theory. There is quite a bit of reason for Blizzard to have such a system from a financial standpoint.