About Riven. What if I told you...
That she was never broken? Riven is probably the hardest champion to play at skill cap and there are only about 6 Riven mains to have reached skill cap with Riven and one of them is faker, and he still messes her up.
The main gripe I hear with her on these boards is that she's resource less. Of course she is. For the longest time top lane meta was heavy tanks, and ranged. You can't spend mana getting to the Mage then fighting him and then getting out while winning the trade nor is it possible for you to kill tanks with mana unless you have insane AD ratios. We could argue the resource thing all day but I just wanted to get that out of the way.
The main thing I wanted to address is her animation cancelling. Let me tell you right now, it is ridiculously hard to do and not mess up. If you're against a riven who is doing it perfectly you're in high diamond + or getting smurfed on. I've smurfed in gold and I've seen the Rivens there, they do not even attempt to animation cancel because they don't know how. If you're not playing against an animation cancelling riven you're playing against a weaker champion. Without cancelling riven is a t3 champion.
Not to be a rankist, but you haven't seen real riven gameplay if you're in silver or gold. The riven mains aren't there, and if you see one he's smurfing. Is riven op when played perfectly ? Absolutely. But no one plays it perfectly, even though they make the occasional perfect play.
Rivens win rate is low now, but she Power spikes harder than ever. I can be 0-3 but when I get my ghostblade if I play well I can still 1v1.
She's balanced around skill, and that's all she's balanced around. If you're losing to her and you're in low ELO you're getting outplayed by a riven who can't animation cancel which is not something you should be admitting to.
If you need help playing against or as riven I suggest you head over to /r/rivenmains