Interestingly, Dr. MacKenzie noted that while a designer should "aim for finality," he also believed that courses were evolving things, and bunkers, for example, might be better placed after the course has opened and there is a sense of how individuals play the course and, therefore, where to place these types of hazards.
I also think there is an element of salesmanship in his statements. Clearly there is an advantage in hiring a first-rate architect to get the job done right, but in their writings, MacKenzie and Tillinghast's tone (perhaps more so than others who documented their ideas) suggests that they are, quite simply trying to make a living. By telling people that they need a first-rate designer, and confindently saying that they themselves are first-rate designers, they had a way of attracting clients for future jobs, whether it be new course creation, or renovation of existing lands.
Tom Doak's statement about the ASGCA seems to follow along these lines as well.