Of course, that friction-induced braking effect is there all the time. You only notice it when you are using it to slow the car down but it is always there. It is there when you are accelerating and there when you are cruising.
The lower the RPM, the significantly more reduced is this friction effect.
This is called "friction"
If your pumping in the gas to keep it turning you'll loose some of the ponies to mechanical friction and receive the rest as torque through the shaft which produces thrust from the propeller. If you lay off the gas the airflow will drive the propeller and the mechanical friction will absorb the energy in the airflow. If the engine has failed you feather the propeller to preserve this energy, if you have a live engine you use it to your advantage to slow down!
Your argument is flawed. Higher rpm equals the propeller taking smaller bites of air with a finer blade angle at a higher rate. Lower RPM equals the propeller taking larger bites of air at a slower rate with a coarser blade angle. The engine does not know any difference! It's still producing 65% power in the cruise via torque from the shaft which is feeding the propeller governor. The prop governor is doing all the work converting the torque from the engine shaft into a set RPM as per what is set on via the CSU which in turn produces thrust from the engine via the propeller.
EDIT
Hmmmm
Having a look at the power graphs from the previous page I pulled two examples.
2500 rpm 22" 66% 124 KTAS 8.8 GPH
2200 rpm 24" 66% 124 KTAS 8.9 GPH
The engine is producing more MP at a lower RPM for the same percentage of power output. I would assume the engine is working a little harder to turn the prop via the governor at a higher RPM loosing about 2" in the process.