A prop turning an engine must be absorbing quite a lot of power, so it must create much more drag than one stopped. How many horsepower do you suppose it requires to turn, say, a 200hp engine at 2000rpm? Lots.
A Freewheeling prop creates vastly more drag than the same prop stopped (unfeathered). A stopped prop only has form drag. A rotating one adds aerodynamic (rotational) drag. All sailing boat owners know this.