It would be interesting to know what this statistic would have looked like in, say, 1980 or 2000. And, of the courses in the top 100 at those points built within the previous 15 years, how many are still in there now. I may be proved wrong, but hasn’t there always been an over-representation of “new” courses in the rankings, with many dropping out of favour later on?
By the way, I’m certainly not arguing that the same thing will necessarily happen over the next 20 years, just that we inevitably look at things from a particular perspective at a point in time and only time will tell whether future generations will agree with us.
One other thought - and conscious I may be arguing against myself here - we may be seeing a different picture in England at least. I’m pretty sure that there are a lot fewer modern (say, last 40 years) courses in the latest Golf World rankings than there were a few years ago. Is that a reflection of us only experiencing half of the equation? The initial boost for courses built in the 80s and 90s is dropping away and there simply haven’t been many quality new courses opening in England since 2005 to replace them. Instead their places have been taken by the likes of Painswick, Kington, Cleeve Hill and Formby Ladies.