I don't like Riven as much as the next guy (usually they feed their asses off when I have one on my team and I can't seem to catch them when they're on the enemy), but I think that this is a good thing for her given what the current state of the game is right now. If you remove this, you might as well remove the speed buff on Ahri and watch as both of their winrates plummet below 45% and effectively killing them.
This is not to say they're balanced, though I do think both are in a good spot right now. You have to figure that we have
who has an ult that traps you, shield that's based off maximum health, and true damage Q plus more reliable mobility than she has. There's also
who is a much more effective split pusher now since he can just ult and walk away.
Just my thoughts, but the way people complain, you'd think the only champs they want to play are

Seriously though, if Skillshot champions are bs and point and click champs have no counterplay, what the hell do you consider balance? AoEs and channels?