Lots of factors influence the outcome of a design and its ability to stay faithful to the architects vision - especially in the long term. You only have to study old aerials or photos of the classic courses to understand that! A great client or committee certainly helps, as does a terrific Superintendent, but after 5, 10, 20, 50 years, roles change, people come and go and your influence in the course set up may diminish (assuming you had any to start with!).
I’m curious to know what % of their work architects feel has steadily improved over time, stays roughly the same or gotten worse.
I would say 70% of our work has stayed roughly the same (some parts have improved, some diminished), 20% has managed to steadily improve and 10% has deteriorated since opening.
One of the quickest and most significant changes can occur with mowing - be it a deliberate change to fit the superintendent or greens chairman of the days eye (or game), or the more incremental 'creep' towards play which can occur over time. Next probably comes vegetation management - or lack of it.