This is a big baseball pet peeve of mine. It has to be a complete and utter myth, logically.
There is no logical way that command and control are different skills. As any pitcher's "control" (call it whatever you want) improves their error radius will just shrink. That's all there is to the whole thing.
Good "command" (being able to hit the corners, etc.) is just exceptional "control" (being able to throw strikes).
I would say, on the 20-80 scale:
20 = no idea where it is going. bounces pitches, hits batters frequently.
30 = cannot throw strikes consistently and often misses badly. high walk rate.
40 = can keep it around the zone most of the time but will frequently miss across the zone. above average walk rate.
50 = can throw strikes consistently, struggles to hit the glove though. average walk rate. control might be good with one pitch, poor with others.
60 = can throw strikes nearly at will, can hit the glove more often than not. below average walk rate.
70 = can throw strikes at will, can throw to all edges and corners most of them time. sublime walk rate; "great command". control might be a bit worse with certain pitches.
80 = elite pitch placement, reads bats and adjusts placement accordingly, can throw any and all pitches with the desired movement and placement. If he's not pitching around someone, the walk was probably the umpire or catcher's fault.