Drag from a stationary propeller is less than from a windmilling one. Think of the windmilling prop as being a disk creating drag.
The problem with Glide approaches to landing is that they are done to runways / marked strips.
Pilots are (almost exclusively) trained to use runway aspect and such things to deduce the glide performance in terms of getting the aircraft in and also use the runway to judge the flare, hold-off etc etc.
Training at all levels provides no information or guidance in the differences experienced when doing a glide approach to a big grass field with no marked runway and no familiar ques for judgement. Hence why people have problems with real engine failures into open fields.
Regards,
DFC