OK Arm - another analogy for you...
Sit down on the end of a see-saw - you are applying a force at the end of the plank but the see-saw plank rotates around the fulcrum. The sitting down force equates to the horizontal component of rotor thrust (or the TR thurst), the length of the see-saw on that side of the fulcrum is the moment arm (height of TR or MR above c of g) and the fulcrum is the c of g.
There is no couple, just a single force causing a rotation.