No idea how people could use KB+M effectively. I understand that people do, but I just don't think I'd even want to play if I couldn't use a controller. Movement is much more intuitive, there's ample room for any and all actions you might need to use and they're all always perfectly within reach and it's fairly difficult to hit the wrong one by mistake (your hand can't be in the wrong position).

That said, I use a mouse for some universal non-intensive stuff like class change and mounts. I also put long cooldown abilities on a column on the left of the screen for reference (though I activate them with a controller).