"Riven is overtuned for the top players!"
Okay, let us talk 'top players', as if that matters to 99% of players. Probuilds is the source of data for professional players in master and challenger tier soloQ.
http://www.probuilds.net/champions/details/Riven 51%
http://www.probuilds.net/champions/details/Jayce 59%
http://www.probuilds.net/champions/details/Kennen 52%
http://www.probuilds.net/champions/details/Gangplank 56%
http://www.probuilds.net/champions/details/Darius 58%
http://www.probuilds.net/champions/details/Camille 63%
http://www.probuilds.net/champions/details/Irelia 51%
http://www.probuilds.net/champions/details/Yasuo 50%
http://www.probuilds.net/champions/details/Nautilus 55%
http://www.probuilds.net/champions/details/Poppy 57%
Hmm... it almost looks like for top players, the best, that Riven and Yasuo are hovering at a nice, fair win rate compared to actual meta monsters like Jayce, Camille and Poppy.
If you are going to complain about Riven doing too well, please don't use top tier players as an example. You'll notice they never complain about her. She is a little too strong in Diamond and somewhat in low masters. She has low win rates below that and fair win rates above that.