Tom,
In fairness to Texas golf courses, the USGA and PGA rarely have seen fit to hold the majors here, and for that matter, hold them most often in the midwest/northeast. Thus, other than his numerous wins at Colonial, yes we picture him somewhere in the northeast.....
On a personal level, I do find historic, or otherwise hard to get on courses stimulating, and often play better there. Perhaps its because I was anticipating the event, and made special time to do it. Perhaps the fact that I'm not trying to embarrass myself and really concentrate may have something to do with it as well. I notice my son plays better at Great Soutwest from day to day with strangers than with Dad, probably for similar reasons.
Who knows what random motivation or distractions influence a round on any day - ie the fight with the wife, sick kids, etc. for both us and the tour pros. We once discussed whether great courses made great champions here, and there are certainly many examples to say it don't make no difference at that level.
By the same token, the theory on the rise of the Europeans was that they played "dog tracks", and were thus more accustomed to inventing shots, unfair bounces, etc. Probably the same with the Texas golfers of fifty years ago. So there may be an opposite correlation as well.
In general, I think the statement is a gross generalization, difficult to prove. I have seen most architects of the Golden Age say similar things. The good Doctor thought hazards "stimulated" better play, etc. Could this be their version of somewhat self serving marketing, as none of them wanted to build an average course either? Perhaps they wanted to stimulate their customers to "build one better than the last one."