I think most architects, say following WW1, were in some sense influenced by the principles of the "art" of landscape architecture. Certainly before WW1 there were a notable few who promoted and proposed it's general principles in golf architecture. Why did they do that? Probably in attempts to imbue golf architecture with more naturalism and a heightened look of naturalism and nature. After all, these were the architects who felt golf should be played in what appeared to be a "natural setting". This was Behr's philosophy and his reasons why that should be so are many, and varied, and ultimately extremely interesting and go far beyond just the art of landscape architecture!
The "art" (or "landscape art or landscape architecture") principles of Harmony, Proportion, Balance, Rhythm and Emphasis were all applied and later basically taught to many architects as a prerequisite of golf architecture.
However, as regards that quotation of Repton that Macdonald and Behr used, there is one facet of it that's interesting and that Tom MacWood singled out on here a number of years ago when that same quote was posted on here.
Tom MacWood said he disagreed with it, and so do I, and I always have. That facet in Repton's quote is that natual defects should be removed or minimized by the golf course architect as they clearly are supposed to be in Repton's conception of landscape architecture. Why is that a landscape architectual dictate of Reptons? Probably because they may be somewhat unsettling or unsoothing to look at. Landscape architecture's principle function certainly is to create something soothing to look at. Olmstead's philosophy is chocked full of many reasons why this is benefical to man. Golf course architecture's function, however, is unquestioable a little bit more than just creating something soothing to look at!
But nevertheless natural defects are Nature's way and nature does not always have to be soothing and settling to look at, and sometimes it probably isn't---at least not as it applies to golf course architecture.
Obviously, if a golf course architect applies that concept of removing natural defects too diligently he will begin to "idealize" the look of Nature in golf course design and architecture and in a real sense that is not benefical for golf and its architecture, in my opinion, and in Tom MacWood's opinion and most likely in Max Behr's opinion, and probably other of the architects who were influenced by his philosophies and writing.
Golf, and it's architecture in the mind of Behr was supposed to be a vying against Nature in about half the construct of the sport (this is actually why he made the distinction between golf as a "sport" as opposed to golf as a "game") and that was supposed to be raw nature, not necessarily some "idealized" version or look of it. On the other hand Behr was certainly realistic in noting a few exceptions in golf and architecture to this principle and philosophy (tees, fairways, greens and sand where sand was not naturall occuring).
The other disagreement I have with art or landscape architecture principles as they apply to golf and golf architecture is this part about "Emphasis". Emphasis in golf course architecture is defined (by C&W) as 'drawing the eye to the most important part'. In my mind if drawing the eye to the most important part is always or generally where the golfer is SUPPOSED to hit the ball, I do not agree with that. Taken to an extreme that becomes golf on a "yellow brick road" or what's become known on here as "shot dictation".
My philosophy is a golfer in what appears to be a natural setting, or a well constructed simulacrum of it, should look out there and be able to decide for himself where he should hit the ball---where he should and shouldn't go, in other words, just as the sportsman in raw nature (the fisherman or hunter et al). Only in this way will he feel he's actually conceived of and executed his own strategies, and when that's done well and done successfully, produces a feeling of mental and psychological gratification in his vying against Nature. In my opinion not much in golf and its architecture is better than that.