So when you arm the motors and throttle up, the apm is looking for feedback from the motors. If you arm and throttle up without blades, will you ever get proper performance out of motors? I am assuming not since the apm expects to move, but doesn’t (regardless of throttle).
APM is an obsolete Flight Controller. Arducopter is not looking for feedback from the motors but the Flight Controller sensors (Acclerometers, Gyros, Barometer, compass, GPS). There is feedback from the ESC’s in many configurations to provide RPM data but that’s not what you are really asking.
Running it w/o props or holding the craft stationary tells you almost nothing other than that they are turning and in which direction. If you want to test the motors use the Motor Test function in Mission Planner or BLHelisuite.