When two things were added to the game:
Dynamic Queue - nobody wanted it. Riot took surveys that were misleading and framed in a positive light without revealing their intentions and used those as evidence that “most people wanted it” (E.G., “Would you enjoy the idea of playing with your friends in ranked games?” without disclosing that this would replace solo queue). Despite backlash, Riot was insistent on this and god only knows why - maybe it was their pledge to launch Esports into its next phase of greatness with League being the premier game, maybe it was pros wanting this for more practice. I don’t really know why. But people hated it and Riot refused to change it for an entire year. And this arguably has been one of the biggest causes of the fractured relationship between riot and its community.
Keystones - considerably less controversial, but they are proving to be one of the biggest disasters this game has ever seen. Most champions were not created or balanced around the concept of something so powerful existing freely to everyone. They are one of the biggest reasons damage is out of control and snowballing is insane. They also are hilariously biased towards offense while defense has one useful keystone. Runes/masteries were simple and boring but it’s because they needed to be. It was out of necessity. They are too gamebreaking and have forced so much powercreep in this game. While they are “cool,” they do too much and need to be straight up removed. You can take a lot of tree’s features now because those are cool without being gamebreaking, but keystones themselves have to go.
Ever since both these things were introduced, Riot’s player relations and the game itself have been significantly worse. And honestly, i think this is also around the same time Riot really dig down and took the “we know best” stance and basically told their playerbase where they can stick it.