question

do you think there is any objective basis for calling a piper or pipemaker ‘great’ or is it possible it’s just something unique about them that we respond to and that others don’t necessarily

in the case of piping I think you could say objectively that someone had total mastery of the instrument - but what is it that sets them apart as ‘great’?

likewise some makers who I have no doubt make first-rate pipes, but who seem to be elevated as having something magical about their pipes, as though it’s implied that nothing else, no matter how good, is equal?

For the first question, I would fall back on a quote from Duke Ellington: “If it sounds good, it is good.” If a lot of people agree that a particular piper is good, I suppose that would elevate them to “great”.

As to pipe makers, if they do make first-rate pipes, does that not imply that anything that is less than first-rate is not equal?
First-rate, in my understanding, would be an attractive, robust set that in the hands of different pipers consistently allows those pipers to produce the music as best they can.

It’s all in the detail.