This doesn't really make sense as an explanation for why it happens the way people are saying it does. I don't understand why it's so difficult to 1) implement a system that is already tried and tested in League and 2) have more transparency about it.
League has a pretty fair and simple ranking system - every game you win earns you anywhere from 15-25 points, you get into promos when you reach 100 points. If you lose, you lose about the same amount, usually slightly less. That's the key idea. It means that if you maintain win rates about 50%, you will still improve.
Over time, as people play, they will end up where they're supposed to and hover around there. This also does ensure a normal distribution, because it still ends up with the majority of the playerbase falling within Silver to Plat, as is the intention.
What seems to be happening here is that games are being weighted very differently to an almost unfair level. If you can win 3 games and be demoted ...