I've seen this chart. It is absolutely fascinating. I can't decide if the courses in the middle years were really so dreadful or if we have changed our attitudes.
I echo your surprise and ambivalence as to what it all means. I had the rare occasion of seeing GD's Ranking issue on the rack today at Stop n Shop and my first wonderings about the clustering of the chart are:
1. As the history of GCA is "only" 120 or years or so, isn't it perhaps quite understandable that there would be peak eras and fallow ones...hills and dales that -- when you chart it up with cultural events like Depression and War and geometric expansions of technology -- make sense? I mean, if we really want to talk about fallow, let;s discuss 1453 to 1860.
2. Which of course, leads to another muse; Golf (though it has a lineage from centuries) and the public enjoyment, spectacle recreation of all "sports" is a relatively new item in the eyes of your World History book...all sport and Golf is a "modern" game, changing from the Open era at every turn....I really think we're all still "workign it out" as it were...
3. The 1930-80 period saw a lot of municipal (not just public) course building -- architecture, that if it was ever even intended for greatness, frequently suffered from crude, laughingstock neglect. So much of this type of building was done in these fallow decades - another rationale for why the chart reads the way it does.
4. The period/decades least well-represented (1940 - 1980) and that almost directly coincides with the pre-eminence of RTJ, with his hard par-easy bogey, heroic cum penal shots, large divided triad greens, requring large care, expensive earthmoving, trim bunkers, Course Beautiful, almost every course a championship course in some aspect. These qualities and features are the opposite of what it is valued today...in the environment of raiders.
So that's the interim question I'm left with from this chart...will the RTJ thesis ever be rehabilitated/refurbished/re-imagined? I understand it's almost diametrically opposed to the thesis of today.