A good machine control system will move the cutting torch around the workpiece, this is what a CNC control system is designed to do. It is different when it comes to height control. The separation between the torch and the workpiece must be maintained at the correct distance. This requires more than simple x-y positioning; a height control system comprises both distance measurement, height control and control of the motor. The tuning of the various components ensures that you get a perfect cut.
Each system should be left to do what it does best, CNC should be used for x-y movement and the height control system used to move the torch vertically.