Crab:
If your rotor thrust (the vertical component of the Total Reaction) is greater than the aircraft weight then the RoD will reduce if you are descending or a climb will commence if you are not.
Precisely! And that is my sole point. An autorotating rotor still has a vertical thrust component. "Vertical component of the Total Reaction" = LIFT.
You chaps are overcomplicating this bit. Nevermind your vector diagrams and formulae. You said it, Crab! In very simple terms, to slow down a descent or to start a climb, the upward force (lift) must exceed the downward force (gravity). Hence, in a steady-state descent, to slow the RoD you need to grab some more lift from somewhere.
Many illustrations of helicopters in forward flight depict a downward flow of air through both the front and rear parts of the rotor. If you've flown for any length of time you probably intuitively know that this is incorrect. In wind tunnel footage that I have seen, smoke blowing at a translated rotor goes right up and over the front part of the disk and does not come down through it (transverse flow, anyone?) until just about the point that it passes the mast. As long as the rotor is through ETL this will be the case, including during autorotation.
The misconception that an autorotating rotor "sees" a predominantly vertical column of air throughout the entire disk is just that, a misconception. Anyone is free to disagree. But some of you lot need to read more. Start with Ray Prouty. I do not make a habit of arguing with him.