Bob,
I could be mistaken, but I think I remember reading about Ross being upset about not being chosen for the ANGC job in the Augusta's Club History book.
Ultimately, it was Jones and MacKenzies' mutual fascination and affection with St. Andrews, where Jones won both the 1927 Open Championship and the 1930 Amateur Championship on his way to capturing The Grand Slam, which sold Jones on Mackenzie.
Also, of note, I remember reading in Roberts book that before they had commisssioned MacKenzie, they went to play Ross' Whippoorwill C.C in NY. When asked whether Mackenzie liked the course. He said it was remarkable. Roberts summoned him to explain. Mackenzie replied, it's remarkable who would be such a fool to build a golf course on property that was not fit for golf. Again, speculating ... but could this have turned there heads? I don't know?