If the majority of matches would have fair matchmaking, you would on average climb higher as a good player.
The fairness of matchmaking is just not a constant, it is changing every few hours or daily. Because the playerpool is simply not big enough. Which we can see by seeing what ranks can even play with each other, just for queues that pop. They gave us easier popping matches, but have thrown out meaning to the ranks out of the window. Which in itself, is not a bad thing. Because it is a game, and we don't want to waste our time. It is just bad, when you pretend to be a serious PvP mode.

You can be stuck in unranked-silver for 100 games, and then clear gold-diamond in 20 matches. What does this say about the game mode? Was it you who was at fault as player? Or is the system just too random, that you aren't able to carry anyone efficiently in lower ranks. Maybe some jobs can do better than others, but even they are not immune.