Great Question!
A few thoughts.....
As far as routing, I learned it early as an apprentice, have a knack for it, and that part of design has probaby changed only incrementally for me in 20 years. I suppose that someone who apprenticed at two or more firms might continue to learn different ways to do it, but eventually would revert to his/her own trademark ways of doing it.
In some ways, most routings are trend followers, not trendsetters. That is to say, if someone gets a walking only course like Whistling Straights, you can be sure that other architects take note of the walking trend, and start routing with greens and tees much closer. Ditto with the trend away from strung out courses through housing, albeit, however small that trend is.
As to strategy/feature designs, I feel those can evolve more dramatically. As we get exposed to more courses over time, and we see just how many different ways you can attack the design over what you may have learned from your mentors, and incorporate it. While routing is a skill, feature design is an art that can evolve.
I'll bet architects go through cycles, at first exploring new things, then relying on tried and true, and then exploring again, when they have started to forget the critiques of the bolder designs, much like MacKenzie!
I doubt you'll be able to trace definitive trends for any architects work, without considering those natural cycles, as well as the budget, client objectives, work load (hard to do your best stuff when busy) personal circumstances (depression, divorce, too much time on golf club atlas, to name three common examples in the golf design field
) and other factors that determine the quality of an individual design by an architect as much as the long term trend of his career.
For example, if Tom Doaks new fame gets him some jobs with real estate developers, or for municipal courses (perhaps the only kind of jobs available in any given year) and he modifies his designs somewhat to fit the circumstances, would you say he changed his style, or did he have to by circumstance? Just as the depression changed the design style of Tillie, Mac, and Maxwell, to name some, our designs will need to respond to the here and now, so that may influence style.
If those courses are less spectacular because of setting, has Tom lost any talent or deep thought about the designs? Of course not! Have his basic influences changed? No, but the influences on any particular design, as illustrated by the examples above can explain a clinker or two in the middle of an otherwise stellar career.