I feel like boxbox kind of proves that wrong. I feel like Riven is good only if you have her mastered, otherwise she is slightly below average. Almost like Azir. They can't buff her anymore because the people who understand how to play her destroy using her, but they can't nerf them or risk destroying her win/play rate. Just have to play around the cc imo.
That being said every time I see a riven on the enemy team I just pick nasus and more often than not I first blood them because they try to fight me in my ranged creeps... Or tower dive me. Some rivens are bad.