I wouldn’t say that most people who call something “overrated” are good judges in that regard, but I think that the implication is meant to be that they don’t feel that the art will withstand the passage of time. It’s time in the limelight is limited and it will not be judged favorably as the years and decades progress.
For example, I just went to our local art museum a few months ago and there was a modern art exhibit. One piece was simply a computer generated tone gradient shift from purple to green or something, printed out onto canvas by a large computer printer. And yet, there it was in a professionally curated exhibit at the major art museum of a major American city. I may be wrong, but I’m pretty sure that in a hundred years time, that particular piece is going to be lost to history (aka, the garbage bin). Its current level of success is beyond what it deserves in my estimation. I may be wrong, but I don’t feel like I’m being unreasonable to hold that position.
There is one possible objective criterion of whether an artist is over- or under-rated - what happens to the reputation of their work in subsequent ages.
Take, for instance, Jane Austen
I would argue that that sort of a reception while she was alive, coupled with her enduring popularity for more than two centuries after her death, means that at the time she was, objectively, under-rated. Whereas someone like, say, Sir Walter Scott, who had rockstar levels of popularity in his lifetime (but you’d be hard pressed to find anyone now who’d read more than one or two of his books, tops) was probably overrated.
So if “Prince is overrated” means anything useful, it should be “I don’t think people will care about him in 50 years time”
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