It's the matchmaking; almost every single game is one sided in lower Elo's. My wins/losses are rarely based on my solo performance, but rather who I'm matched with. Sadly it doesn't balance out till higher up the ladder. I remember I had easier wins in Gold 2 Last season than I did in all of Silver from the consistency of players alone.
I'm seeing team scores going 30-8 most games, with every single lane dominating by almost double performance. Half my wins I don't even feel like I deserve. I've gotten S+ games for doing less work than I did in games I got B ranked all on the basis of who I matched with.
The reason you notice it more this season is that Riot wants 20 minute long games, and most champions snowball of one kill now. Put a game that rewards you with being ahead on top of a really "Outdated" system and yeah you'll notice it a lot. Even a slight inconsistency in player skills can decide the game before it even begins. Your solo performance means a lot less this season compared to others.