I gotta say that this is annoying. I currently work for a place where we're all Macs and iOS. Many, many devices all over the place, all broadcasting for AirDrop and AirPlay. We're a school, they are useful features. Everything connects to a mesh wifi network. Neighbouring APs are of course on different channels.

It's like we're the perfect environment to experience this problem on a massive scale. We've tested and replicated OP's test results. So now we have a choice between good wifi and AirDrop/AirPlay? This sucks.