Riven is balanced.

I'm just kidding, she's literally a champion that Riot overdesigned for the sake of "skill expression", one of the dumbest and mind numbing concepts in all of League. She has multiple dashes, knockups, stuns, and shields in her kit that are literally free. They don't cost mana, energy, or any resources. Most people say her cooldowns are long but in reality she has regular cooldown timers. Not only that, but she has plenty of items and runes that she can take to adapt to just about anything. She is almost never a bad pick, hence why people one trick her, and her ability to basically steamroll teams is practically unparalleled.

People want to talk about how Yasuo is broken, but Yasuo actually requires a lot of skill to pickup and play. Yasuo also needs a lot of gold to start up. Riven on the other hand can dominate people with a couple of longswords. The whole idea that Riven is hard to play is sadly a myth. She is an absolute nightmare to lane against because she generally dictates matchups. If you want to engage on her, she can disengage. If she wants to engage, she will usually find her way to you. Her damage once she is on you is pretty much unavoidable as she has knockups and stuns that are generally meant to keep you locked up. And if it doesn't make things worse, she has an AD steroid that makes her hit harder and allows her to kill you should you run away.

Essentially she needs to be looked at and given the Irelia treatment. Maybe the Akali treatment too. She is essentially a fraudulent champion and overall the idea of powercreep and mobility creep personified into a single champion. Even Yasuo, the arguably most hated champion in the game, is less frustrating to play against.