Why is Riven a champion

I have been playing league since well just over the summer. It seems every game that i get into with a Riven she gets fed. I am not talking the usual adc handfed kills fed... No i am talking 15 plus kills every game with like 2 deaths. I have watched a bad Riven walk into lane against a good renekton and get 5 kills... She has insane mobility and a crazy shield and not to mention her animation cancels... Riot why did you have to make this champion ins the place of Omen... Im sure majority of the summoners would have loved to see Omen over Riven. I almost forgot that nearly all Riven mains are insanely mad about everything. You give up first blood because you got 4 man ganked in the beginning of the game and here she is screaming in chat that you suck at the game and you should uninstall the game and never play it again. Riven mains also still have the highest leaving rate in a game of all other players... Up vote this if you would love to see her get disabled again or just have riot nerf her so all the Riven mains get butthurt.