Why do i feel like every time i play league im getting worse?

Before season reset I mained vayne. I was bronze 5 at the time and I was doing pretty well with her. I was getting pentas and carrying my team and three shotting everyone. After preaseason, I hit silver 5. I was once again easily climbing destroying with vayne. I made it to silver 3 with ease and was holding my own up there. Those first couple of weeks I played with mostly people who were gold the previous season. I felt like I should be gold because I was carrying my team against other golds. Then a couple weeks later, once all the people in gold climbed back to gold, I dropped rapidly. I was playing against fellow silvers, but I was losing. I couldn't understand why people became good all of a sudden. I ended up with much harder laning phases. Did people learn how to counter hypercarries in lane by then?? Did the warlord's bloodlust and static shiv + firecannon nerf hurt vayne a lot more than I thought?? I feel like I can't get in range to deal damage in teamfights either. Leona goes in, I go in, I get 4 shots off on the enemy front line and an enemy brand standing right next to his frontline trundle nearly one shot me. Should I have better peelers? Do we need a better fed assassin? Did Leona not have enough cc?