I suppose, I always figured that 10 ft. lbs. was an average over 720 degrees of rotation on a 4 stroke, and that all the force required to maintain that average was developed over 180 degrees (ignition stroke). For the other 520 degrees the motor is developing varying levels of parasitic drag.
In addition, I always used the output side to lock if a stock flywheel key was specified by the rules. If you lock from the flywheel, ignition timing will retard during tightening. If you lock from the output, timing will advance during tightening, so you'll end up with the max timing advance legally available.
JMO