It's interesting that this debate is all about drag.
I say interesting because it is not drag that matters in determining the sink rate in a glide. It is the power required.
Its not the drag that matters.
Its not the power required that matters.
Its the power required per unit weight of the aircraft that matters here, this quantity has a direct relation with the all so familiar Lift to Drag ratio.
Heavy car, top of hill, release brakes, will be going faster at bottom of hill than light car due to stored (potential) energy!
It's no more complicated than that!
My instructor always stressed on Keep It Simple and Stupid. But this is analogy way too simplistic.
You have controls in aircraft using which you can set its speed for a descent.
I haven't seen any car with down the hill cruise control while in neutral gear.