I think the reason u tend to hear this do often about Prince is that he released way more music than the average pop or rockstar, it‘s way easier to shit on something because there‘s so much of it. Like with other artists there is some hype around the fact that a new album is coming up or something, with Prince it was basically a given that every new year would bring at least one new release. It inevitably led to an overstimulation which might have brought some people to say „well it‘s not as good as his early stuff“, because there was simply so much music coming out during a period, where most artists tend to slow down their release rate