I'm seeing a repeated pattern in my matchmaking

People often say that it's a myth that Riot pushes you toward a 50% win rate. Do I have proof? No, I don't take the time to write out the win rates of my opponents and what there streaks are like versus my teammates, however, with that being said, I can tell you from memory and experience that I feel, this myth is no longer a myth, it's truth.

Over the course of the past couple months, I have had large swings in MMR and rank. The first swing was at the start of the season, I went from being placed at Silver 4, to Plat 5 with a higher than normal MMR, Then I was stuck in Plat 5 for a while.

Then the next swing, I went from Plat 5 to Plat 2 very quickly, what happened then? A series of loss streaks that put me at a 50% win rate to Plat 4.

I then had another swing. I went from Plat 4, to Plat 1, very quickly. What happened next? I got a streak of losses that put me at 50% win rate at Plat 3/4.

I now just had another swing, before I did, I got demoted to Plat 5, then I quickly shot up to Diamond 5 90 LP. Can you guess what happened now? After hitting D5 90 LP, I had 17 losses in 20 games. Yes, some were my fault, but most were mistakes my teammates made that I could not control. I have now demoted to Plat 2 75 LP, for every one or two games I'm winning, I am losing 3-4 or even 5. I fear that this loss streak won't end until I'm in Plat 3.

I don't understand the meaning of this, I know I am a skilled player, but how can a skilled player that can play good at D5 with higher than average MMR (Playing with Diamond 4s and 3s) get such loss streaks to put them way below where they belong?

I seriously think Riot pushes people toward a 50% win rate, it's annoying, and it's stupid.