Thanks for proactively trying to solve a frustrating situation—and coming to Meta to discuss solutions for it!
My opinion here is that hemisphere-wise, continent-wise, region-wise and country-wise breakdowns of tags are (mostly) too broad to be useful, if used for the purpose of music categorization.
A lot of music is global in nature. Genre tags work far better to classify such music compared to regional tags.
European music is vast and varied (and Europe is one of the smaller continents!). Very little is to be gained by sorting questions by continent when a specific genre tag would do the job much better.
A good rule of thumb for checking if a tag is too broad is to ask whether there exist experts in that field. (The ID tags are a special case, let's keep them aside for this point.) I think it is highly improbable for a person to be an expert on all of European music, so classifying music using a [european] tag is not helpful.
To address some of the other points in your post and the comments,
I understand that this site is fairly slow in terms of new questions, and for that reason it is probably best that we keep taggable topics fairly broad.
My conclusion is actually the opposite. I think it would be great to have specific tags for genres and artists as they keep arising, without waiting for questions to build up first before introducing the tags. I wrote up some of my thoughts here earlier; in brief, my feeling is that specific tags are more helpful in the long run compared to broad tags — as the number of questions on our site increases, the broad tags will become more and more redundant just as the specific tags will become increasingly useful.
So if a question is tagged with both [european] and [metal], someone who calls themself a metalhead but is only an expert in Nickelback knows not to bother answering. Same goes for a question tagged [european] and [folk]. Someone who thinks they're an expert in folk because they can sing '99 Bottles of Beer' will know they're not 'the right man for the job'.
And therein lies what this tag gives us. A new way to distinguish between very different styles of music. What does lumping American metalcore with Swedish DSBM (depressive suicidal black metal) do for us?
Optimising for exclusionary filters is maybe not ideal at this point, given the current level of site activity. But I think this is actually a great argument for introducing more specific artist and genre tags!
All this being said, I think that country / region / continent tags can work under some conditions:
- Trivially, if a country / region is "small" enough that its indigenous music is synonymous with the genre of music that comes from there, then such a tag works—simply because it's a disguised genre tag.
- More interestingly, if a question specifically involves or asks about the cultural and historical background of a country / region / continent, then tagging it with such a broad tag would work well. For instance, music in India is also highly varied, and a (hypothetical) question whose context involves the cultural background of the country/subcontinent would benefit from an [india] or [indian-subcontinent] tag, rather than using all the genre tags that may be vaguely related (or worse, using none of them).
I don't have a specific example of such a question already on this site, though.
In your question, I think tagging with the genres and artists serves a better purpose than the [european] tag, since it's only a two-way comparison, if that makes sense.
It also seems we lack a tag for questions that ask about or discuss melodic comparisons (as in your question). Off the top of my head, I think we're currently making do with a patchwork of other tags, which is not ideal. It might be good to collect data and propose such a tag on Meta.