Looks alot like Wild Bill Melhorn's stuff. MacDonald might have been influenced by Melhorn, many were in the 20-40's.
MacDonald may indeed have knocked off Mehlhorn. Or perhaps vice versa. Or maybe both knocked off Vardon. One thing's for sure, Mehlhorn had no book ("stuff") at that time (1927) and didn't for another sixty years.
Or just maybe the way most of the 'old guys' taught the game was better than the way most of the 'young guys' taught the game when I was coming up. Trust me, the Exercises produce a far different Stroke than the conventional instruction fads of the 1970s and 1980s, e.g., a weak grip, exaggerated leg drive and the 'reverse C.'
The reader can decide for himself whether or not the MacDonald Exercises are superior to the present day instruction. As a yardstick, pick up any half dozen of the latest golf releases -- books or magazines or both -- and see which ones have you moving most correctly most quickly. As an acid test, see which one the golf ball likes best.
Whatever...
The MacDonald Exercises constitute no less than the Basic Motion of the Golf Stroke. Get them exactly right, and watch your scores go down.