So i guess we're back to the "i'm better than you" argument, did you know that it takes a tremendous amount knowledge about your class to multi-box it well?
Sure, i have a shaman/druid setup, the most OP one of them here, but i ran a feral setup on WoD because it was fun to run around with that, i'm running a dk/monk one in legion because i like the challenge of how to make a tank/dps/healer working, and thinking about start a mixed PvP/PvE one here.
I could be like Prepared and click one button that spams Arcane Explosion on a mage, Moonfire on druids and so on(no offense to him, it was probably more, but didn't look like from his stream), but actually getting to the point where you can comfortably line up different abilities/procs on classes, that takes a good while and skill for that matter too, i have about 40 different keys with different abilities, some for just throwing the ability on all, and some cast sequence them on different subsets of characters, i would guess if any person that doesn't multi-box were put at my setup, even if they could change the key binds to their own, they wouldn't be able to do it within a week.
Multi-boxing requires such an extreme amount of multitasking(to be good at it) that quite frankly i have times after i've been in a Wintergrasp, or a city defense, i just go and fall asleep for several hours because my brain was running at full speed almost all the time.
So could we stop talking about the fact that you're better than me(us), just because you play one character at a time?