Riven is a terrible champion right now, every type of item she needs has been changed in a way that no longer works for her (CDR decreased, increased in cost, raw AD decreased in favour of crit, etc). If her win rate is ever around 50% the whining is endless, if it's below it they still say she's OP half the time even though her stats mostly come from mains which actually bloats the number compared to other champions who don't have as many mains.
Here's something the low Elo shitters won't tell you: Riven is quite likely the highest skillcap champion in the game and almost no one can properly make use of her animation canceling. There's a thread every day bitching about her being able to do that when most her power budget is actually put into that, as in her other aspects are kept super weak because she does have such animation canceling. Here's the kicker: Not a single one of those whiny mongos has ever encountered Riven properly animation canceling in their shitty low Gold to Bronze 5 games.
Most people I encountered who thought they were doing it right were actually not saving any frames, they were just clicking and achieving nothing. I have yet to encounter anyone from low Plat to low Diamond who does it properly. Unlike almost everything else in the game, her animation canceling being done with proper timings AND spacing (to make it worth doing as opposed to a net gain of zero) requires quite a bit of muscle memory and reaction time comparable to a fighting game. That's saying a lot for a game like League where people regularly played with over 100 ping because it requires no reflexes for the most part. Riven is the exception to the rule.