Mike,
I just re-read your articles and found them to be very interesting, especially the rift that developed between Travis and Macdonald. As you correctly conclude, what actual influence Travis had on what was laid out at NGLA cannot be determined and it is a moot point anyway: Macdonald was in charge so he gets full credit for the final product, including good ideas that his assistants may have provided.
I was not trying to be dismissive of the work other architects had done at the time. Rather, I was trying to provide an answer to the original question: why did the (very popular) Macdonald/Raynor style disappear? I stand by my thesis that it was the Depression, the death of CBM and Banks, no work for any of their assistants, and a huge time lag before there was a lot of new construction work.
One of the interesting things I found in your article was Travis' criticism of NGLA as being too hard, too overdone. That allows us to make two conclusions: CBM made final decisions that Travis did not like, and what was built at NGLA was truly unique. So it is not hard to envision Macdonald boasting that he built 18 great holes, implying his ideal golf course was far better than Garden City, Travis bristling, and replying by saying CBM simply built 18 hard holes. Then Travis goes on to say, by the way, the holes are actually poor replicas of the originals! Gotta love that!