False...
A closed loop stepper of the same rating (i.e. 1200 ozin) will provide the exact same motion or propulsion of the machine. That said, most closed loop systems will exert 100% torque of the motor once a threshold (usually one full step) has been crossed. Depending on the actual torque being used at that moment, this may get the axis baxk on position, but not often enough. Should the closed loop stepper exceed a user set threshold, the drive will "alarm". If connected properly, that alarm will stop motion for all axes.
Other than ability to stop motion and allow the operator to make a correction, the cutting ability between the two are insignificant if the toolpath parameters are within the torque limits of the motors. The reality is, if you muff the toolpath parameters enough to loose steps, you will loose steps. The closed loop system should stop, not so much for the plain stepper.