ADC's are the Riven-mains of all classes
Think about it. This is just a comparison of people's reactions on these boards, and you can think about Riven however you please.
You got your generic "OH HOH HO RIVEN IS SOOOOOOO BROKEN" people on the boards who realise Riven can easily deal a quick 2000 damage to enemy carries whilst having free mobility, shields, cc and even bonus damage!
And, you got your generic "OH HOH HO ADC'S ARE SOOOOOOO BROKEN" people on the boards who realise ADC's are allowed to deal large amounts of sustained damage while getting small healing off of it and usually being at a safe distance.
Then,
You got your generic "Riven takes a lot of skill and practice!!!!!" people on the boards who try to defend Riven based on her "weaknesses," such as her high skill cap and high punishment towards idiot riven players who don't have 7 ping and don't auto between abilities.
And, you got your generic "ADC's are squishy and pop like a balloon!!!!!!" people on the boards who defend ADC's based on their weaknesses, like
, which can either be played around by the most professional of ADC's alongside the most professional of supports, or be the simple, easy cause of their quick, easy defeat.
Now, that's the biggest similarity between Riven and ADC's. It's case of Schrödinger's Riven/ADC. A Riven can either be really, really bad, or really, really good. An ADC can either be mediocre and get absolutely stomped by the items/spells/champions listed above, OR, they can either be really good and play around it, have a strong heal/shield support to keep them alive during every other champion's high amount of burst, or simply not have to play against anything of the sort. The only reason people think Twitch is any good is because he can gain exxxtra long range and the element of surprise, since most other champions are brain-dead and just hope they can see the ADC so they can easily jump on them and instantly slaughter them.
The main difference between Riven and ADC's is the one fact that should deflate the entire "Plz nerf ADC's" argument in itself: #Both teams get an ADC. Both teams are given the opportunity to deal high amounts of damage, both teams are given the opportunity to COUNTER the ADC's, and both ADC's are given the opportunity to be good and work around every single counter Riot has thrown at them.
But the sad thing is, these boards will only be happy if BOTH ADC's get countered. If one of them gets countered and the other one carries, the boards will cry about "Oh boo hoo, so much damage." If both ADC's are good enough to carry, the boards will cry about "Oh boo hoo, so much damage!!! League of Carries!!!!!!!" until Riot finally nerfs the ADC's again, and again, and again, and again, and again.