Tim,
You make a salient point, that the bunkers we see today are not the ones that Morcom & others initially constructed.
The bunkers at RM have certainly changed shape over time. As you suggest, the lips of some have been raised by the frequent blasts of sand. However, rather than becoming more complex in shape, many have tended to see their form lose detail: islands have disappeared, smaller bunkers have been amalgamated... Also, whole bunkers and even entire clusters of bunkers have been filled in.
The bunkering of the 5th hole of the West has changed significantly from its' original form, but more for reasons different to those you suggest. I know of aerial photos from 1931, 1936 and 1945. In 1931 bunkers extensively covered the right and rear of this green; there was a small front left bunker; and an open area to the left of the green (though it's hard to tell what this area was like, it doesn't look like a bunker). By 1936, the left and right bunkers had broadly taken the forms we have today, but there was still a large rear bunker. By 1945 hardly anything was left of the rear bunker, leaving the basic structure we are all familiar with: strong bunkering on both flanks. Clearly this is a big change from the constructed form that Mackenzie supervised.