The thing about ADC is that while it is overturned right now due to item prices, they still require skill. No other class in the game aside from assassins is so position and mechanically intensive. And you say "right click mechanics" try and stutter step at 2.14 attack speed with only right clicks in a minion wave. "But that's not normal" yes it is, most ADCs that go double Zeal get above 2.0 attack speed because of Zeals, Grieves, and maybe runes plus Bork. Not to mention they are a generally low mobility class with very little survivability besides hope your team cares about you. You say that marksmen are low skill, what about Sona, Soraka, Malphite, Maokai, Xerath. These champions either just sit back and hit the same spell over and over again, or go in and face roll while being hard to kill. Marksmen are not hard, but they are mechanically intensive in a different way. Going from one class of champ to a other, how many of an ADCs mechanics transfer? Not many because there are very few solely auto attack based champions. Yi, Xin, and maybe a few others.