They can have something to say about the impact of a class. If a class has no champion that has either extremely high or low winrates, then
A) The champions are balanced relative to the role
or
B) The role has little impact, due to the fact that it does not matter the champion strength, the role will still have the same impact.
However, ADC is in a weird position. The only times winrates in this class are really high is in the case of either insanely overtuned champions who are hard to lose your team a game with(
pre nerfs), or champions who can have major teamfight impact (
pre- meta shift).
Aside from that, ADC statistically has no really high winrate champion. However, there are really low winrate champions.
This leads me to believe that your ADC pick does not matter unless it is not super weak. This most likely means means that ADCs do not have a huge influence on whether or not they win the game, but poor ADCs can easily lose a team the game.