ADCs are being used to dominate Jungle by smurfers
So can we now admit that there's a major problem? Multiple smurfs popping up with Twitch/Kai'sai Jungle, and hitting high dia/masters with extremely high winrates on these champions. In the past such feats would be reserved for champions such as Yi, Nidalee, Zac, Shyvana or Elise - all dedicated Jungle champions, but they're now being outdone by champions whose main role is ADC.
When champions whose dominant role is ADC start to out-do Junglers at their own role it becomes clear as day that there's a major problem. Especially considering that the Jungle requires strong 1v1 duelling ability, which is what ADCs SHOULD be weakest at, yet they're still nonetheless succeeding. It also requires certain other traits that ADCs shouldn't be particularly effective at (barring Kindred, who was made for the Jungle), yet they're still not only succeeding, but DOMINATING.