OK arm, what happens when the c of g moves (it changes horizontally, vertically and laterally as you add or subtract fuel, crew, pax, internal or external load). If in your diagram, the c of g has inconveniently shifted itself so it is towards the port side of the aircraft then your couple between weight and rotor thrust will keep rolling the aircraft over.
If it is the relative positions of the main and TRs that dictate hover attitude, then why doesn't an R22 (very high rotor mast and low mounted TR) hover 15 degrees left wing low?
Saying that the c of g is irrelevant in the opposing couples is like trying to make a lever work without a fulcrum. Every control input you make creates a force that acts about the c of g to achieve the desired pitch roll, or yaw.