I am a long-time player and while yes, the client has problems I think it's not AIR's fault. AIR is fine, maybe not perfect but it's not a good enough reason to ditch all the apps that are made with it. It's like saying "I will not browse any website made with PHP".
Would you like me to show you some terrible programs written in JavaScript? Any platform that has programs written for it has bad programs written for it.
It is true that League of Legends players generally think Adobe AIR sucks. It's also true that League of Legends players generally think they deserve to be at least Gold I. In neither case are these beliefs rational.