Could be, propeller drag has multiple definitions. I think you are right but not completely sure. I mean this is kind of, but not entirely:
Emphasis is put in the friction of engine components, while this is related it is not the core of the problems we are facing. I think his explanation is mainly about the relationship between drag of internal engine components and windmill RPM.
IF it is simulated at all it isn’t simulated accurately as it is way too weak, especially on turboprops. I have flown the Kingair in real life, the deceleration is nowhere near what it should be. Also on single engine piston aircraft it isn’t accurate in my opinion.
I did run a test couple of updates ago, so maybe I need to rerun it, but on the TBM there was absolutely no difference between flight idle, prop feathered (or at least feather selected) and full reverse in flight.
I also ran this test (although long time ago so maybe invalid now):
I don’t remember what Seb said the L/D ratio was of the TBM yesterday but I believe it was around 16/17 for just the airframe, so glide ratio around 18 is not too bad (for just the airframe! Not taking into account propeller drag). I will test it again tomorrow and see if it is still the same.