My problem with understanding this is that an increase in RAF produced by this increase in rotational velocity (Vsquared) would create a greater amount of 'lift' and a consequent increase in torque (drag) and the status quo is returned. Neither does this consider an increase in alpha as a result of the increase in RV....
For a typical propeller aircraft, the propeller's rotational speed at the most effective part of the blade (around 200m/s for a light aircraft) is much much bigger than the forward speed (around 50 to 100m/s for a light aircraft).
Therefore, an increased forward speed produces a proportionally large reduction in propeller blade alpha with only a proportionally small increased airspeed experienced by the blade.
A large reduction in angle of attack with a proportionally much smaller increase in speed will have a very large effect on lift & drag, as you've already said. So, the blade will be "unloaded" and will increase RPM. Because rotational speed is (usually) much bigger than forward speed, a small change in RPM will restore the balance that existed before the aircraft accelerated.
I really wish I could post a diagram!
Cheers,
O8