Edge was a Buff to her laning phase, which is the most oppressive phase of the game for her. A free 10% boost in damage while making your ult do tons is way too strong, but you only got it when you were in lane. In real team fights, Edge was near impossible to pick up, especially since your passive stopped stacking to 3 and it required you to AA with your passive up, thus ruining some of the more popular 2 Q's and R, then Flash and Q+AA+W+AA+R for a ton of AoE damage. Also made her counterplay into 'We picked this sorta champ and you're now completely useless because you have no edge, ever' like Syndra and Ali who simply knock her back mid-Q so she can't stack her Edge. A lot of Rivens will tell you it's hard to make perfect use of the passive in a team fight with CC happening and knock backs and snares are Riven's biggest weakness since knock backs can not only stop her Q's damage, but also make it to where she has to use her Q to get in close again and snares of course make her Q and E complete unusable for the duration so she's just a sitting duck.
Overall, her snowballing was skyrocketed through the roof with the Edge system while her team fighting was gimped, which is the complete opposite of what champions should be.
