Most other games have training modes or other features that allow noobs to learn the system. WoW isn't as transparent as those games and needs some sort of advanced tutorial system. The game definitely has gotten more complicated since vanilla to the point where it must be overwhelming for a novice.
Staying out of fire/dust/voids doesn't change in complication from when they were happening in Vanilla to when they're happening now. Boss fights are also significantly less complicated than Vanilla.
Do you see any bosses that can wipe an entire raid with chain lightning? No? Because C'thun could, and still can mangle you for 1million nature damage on a random cast that you have to be constantly aware of your range from the other 39 people in your raid, for the entire fight.
39 people's range for chain lightning, not 4 people for getting out of a dust cloud on the first boss in Stonecore.
Every boss in heroics are either "stay out of the stuff on the ground", "move away from the aoe", or "take out the adds". There is nothing remotely complicated about boss battles in these heroics except MAYBE that dragon in Vortex Pinnacle.
If you're referring to class play as being more complicated, yes, I'm sure REDUCING the talent trees significantly made classes more complicated.....