I don't agree that de-ranking needs to go, just that the matchmaking needs some fixing to be much tighter than it currently is. I have gotten from Plat 1 to Diamond 5 3 times so far. I think the system they initially started out with worked the best (Dia 4 or 5 will get matched up with max. Plat 1 or 2 iirc).
Currently, each time I manage to get up to Diamond 5, either one of the following happens:
1. I get matched up with Plat 4s that just dive in and try to 1v5.
2. I get matched up with Crystal players that are on the top 10 of the leaderboards.
Obviously in case 1, it's a loss because you cannot 4v5 a match. In the second case, a win or loss is a coin flip. I definitely don't think I'm able to compete with the top 10 of the leaderboards, and at the same time I'm probably ruining their matches by not being good enough.