Is very true. If you are holding down one of the mouse buttons to rotate your character or the camera, the cursor cannot be used to interact with other interface elements.
I can't believe this "argument" is still dragging on. Clicking abilities is like typing with oven mitts. Can you do it? Sure. Will any amount of success on the part of an individual ever change the fact that it's incredibly inefficient? Nope.
That being said, yes, the OP is wrong insofar as clicking doesn't automatically mean you're bad at your role.