Actually, I do find it interesting. I suppose it has mostly to do with expectations. Younger pianists are expected to ripen into masters, and those whom have ripened into masters... well, where do they go from there ? I think most of those types of expectations are based on the premise that an individual reaches his/her full potential at a somewhat isolated period of time in their life and in an isolated kind of way. The younger ones are still expected to move into their fullest potential, while the more mature are expected to move out of it (which does not make much sense to me... why continue living after a certain point ?).
In some aspects, today's mediocracy is yesterday's excellence. There are many phenomenal players these days of all ages and races. What was once considered spectacular and rare, is not quite so anymore. So there becomes a different context in how a pianist gets judged by the people.
As far as judging a performance as an independent occurance, I think it is theoretically ideal, but fundamentally impossible. There is always some kind of context and some kind of ideal involved when it comes to "judging".
If the idea is to stop accepting mediocracy altogether (which I feel is your actual point), whether it could ever happen or not, I more so just don't see how to go about it. Whose standard sets the tone for mediocracy or excellence ? Maybe we should just stop judging ? I am not sure that would lead us out of mediocracy. Also, independently accepting a person's best efforts as excellence, because that is the best they could do on that day at that time, is not necessarily avoiding mediocracy either.
Maybe in the end all we have is mediocracy... LOL (I think I need to get more sleep).
m1469