Let's go back to early days of League to explain this.
Caitlyn and Vayne were polar opposites when it came to playing them. Caitlyn was an absolute goddess in the early game and had great power in the early/mid game. However, the longer the game went on, the worse she was. At late game she was pretty awful and could barely do anything. Conversely, Vayne had an early game that was a toothpick under toenail tier. She felt terrible to play. By mid game she started picking up and finally, in the late game, she was tumbleweed nuke with silverbolts on a stick.
You'll notice that these characters have almost inverse proportions these days. Caitlyn's early game was nerfed in exchange for her late game power boost. Vayne is now not awful early but still has a decent late game.
Riot's necessity to "feel good" has caused great balance problems. And yes, players are partially to blame as well, but I put the onus on Riot for listening to these complaints. Champions SHOULD have high and low points and there should be trade-offs for having decent-to-great phases. If I lose lane as Caitlyn, I don't deserve a decent mid game and a great late game. Likewise, if I can weather the storm, I should get a reward for playing Vayne. This is also a very important balancing lever: Carries need weak early. Lane bullies need weak late. When everyone is decent, it just makes it about who is the outright best, which leads to metas where you have about 10 good characters and 2 great ones.
Really, there needs to be bad feelings in league. If we don't have them, how can we really tell when something is **GREAT**?