I think judging the craftsmanship of music is significantly easier than talking of proper aesthetic judgments (where neither might be subjective contra a widely held opinion). That is simply because we follow certain rules of compositional writing when we make judgments about its craft. Someone might be able to write excellent fugues, and we can recognise that (and an expert might recognise that even better!), but this does not mean that an expert is uninterested in the aesthetics. What is a good fugue worth, if it is not backed up by proper aesthetic choices?
So I think that, ultimately, while you are right that craft can be easily judged, such judgments would be relatively useless when separated from aesthetics. I deeply doubt that experts who judge music do not care for aesthetics. Similarly, an artist might have excellent technical skills of painting but when they use them to paint something disgusting, those skills hardly amount to anything of value. Sure, an expert might recognise those technical skills but I hardly see what help that would be. For this very reason, I also think it's rather questionable to think that an aesthetic judgement of someone who has no knowledge of the craft is useless or means absolutely nothing (it certainly means something!). I mean, useless for what? What is the use even supposed to be? (I don't think we ever think we are doing something particularly useful when we make an aesthetic judgement--rather, we simply express something and that need seems to have to do with human nature, not with anything pragmatic.) An expert opinion about the craft is not going to overturn someone's aesthetic judgment and the latter is, in the end, important.