@dc42 Several reasons.
One, it does not appear to know which motor is associated with which point on the grid. Thus, it does not appear it would actually know which motor to engage to move a corner up and down so that it is level with the other three, it moves the whole plane to account for it. No different than bed mesh leveling
UNLESS, it is required that each of the assigned motors be in the same clockwise orientation required by the probing...
(Whoops. Here it is the process documentation. you linked. I will have to rewire the motors. Ah well. Unless when I define the motors I can put them out of order to match the wiring, like Z1:3:4:2 )
You must use the M671 command to define the X and Y coordinates of the leadscrews. The M671 command must come after the M584 command and must specify the same number of X and Y coordinates as the number of motors assigned to the Z axis in the M584 command; and these coordinates must be in the same order as the driver numbers of the associated motors in the M584 command. The M671 command must also come after any M667 or M669 command.
Although the second issue remains: it throws warnings that this method is replaced by the bed mesh leveling method.
Will there be a bed mesh compatible version of the independent Z axisitalicised text