What is wrong with matchmaking?

Steamrolled every game this season got plat 4 with a 60% win rate. Suddenly my win rate plummeted. I started getting hard feeders every single game. Every lane went 0/5. I'm wondering what the fuck?

Well after looking into my match history it turns out that even at plat 4 with a 60% win rate I was being matched with gold 4s and even some silvers. People who haven't done a single placement game.

So what the actual fuck? Why do I have people who have literally never played ranked before in my plat games? My win rate has plummeted to 50%. Had I known that plat elo was going to essentially be silver I would have picked a different role and carried out as something like jax. What the fuck is this matchmaking?