ADC's are actually pretty balanced right now...
Before you downvote this, please read what I have to say. Obviously there are some adc's that are more broken than others, but I believe the class as a whole is pretty healthy right now. The real problem is lethality. If an adc gets a lead, they can easily build lethality because of how cheap the components are, and then proceed to snowball even harder. Also, I know it's not a lethality item but death's dance is a big problem. If someone starts to snowball, it's almost impossible to shut them down once they get this item. The amount of free stats this item gives is absolutely ridiculous. ADC's are supposed to be late game champs. Their items are supposed to be expensive and they don't really start to become a threat until late game. If you want to nerf something, nerf lethality (and death's dance) please.
Also, Riot doesn't love adc's nearly as much as people claim. If this was the case, why do jungle camps reset now? Clearly they wanted to make it harder for ranged champions to jungle, and they succeeded in doing so.