I just don't see how Draven is demanding with positioning when his strength is his ability to just sort of to hunker down in place and destroy people with unmatched damage that has absurd scaling with lifesteal.Draven is very mechanically demanding in team fights, you need to have really strong positioning and the ability to juggle two axes in a high pressure environment as well as not having any reliable escape mechanisms.
Other than Vayne, and perhaps Kog'Maw, I'm really not sure what ADCs are more mechanically demanding, especially strong ones. MF, Ashe, Caitlyn, Varus, Ezreal, Graves, Tristana are all much easier to play.
Twitch and Corki are probably on par, or less mechanically demanding.
I think you're really underestimating how easy other AD carries are compared.
I am not really huge on citing stats but Draven is obviously one of the most popular picks right now with a super high win rate. If he was so mechanically demanding I don't think this would happen. This is true even at a bronze level, and the only other popular champion with such a skewed win rate in their favor is Janna.
You are underselling the difficulty of other carries. If you miss a skillshot on Graves you're screwed. Tristana is super hard to play properly with specialized abilities until you get to late game. Other carries are much more reliant on proper ability usage and kiting/positioning requirements.