Calling it now this app will be quietly discontinued by 2025. Doesn’t justify the engineering overhead for a different meta data grouping/filtering. None of this sounds anywhere near as complicated as people are making it out to be.
I've been growing and maintaining a collection of classical music for ten years now, which means I've been trying for ten years to solve this problem with tools designed for the same use case as Apple Music. If it were as easy as you claim, then by now I would have solved it at least well enough that taking a physical CD off a physical rack and putting it in a physical player never felt like the more convenient option.
If the app's discontinued in a couple of years, it won't be because it never made sense to build, especially given that I'm sure they're reusing most of both the frontend and backend for Apple Music as it exists today. It'll be because they're addressing one of the world's pickiest audiences, and not succeeding in getting enough right enough of the time - on that score I wish them the best of luck; on every other, I don't think I need to, not least because they might well succeed in selling me an Apple Music subscription with this.
I am just struggling to find a need to have a separate app, I guess UI/UX perhaps but I still echo the same fear as the parent commenter. I am sure Apple has the money to support it, and while I love classical music, I am not downloading another app just to consume it.
As I said before, I've spent a decade trying to solve this problem with the same kinds of approaches you're advocating here - that is, using tooling built for general music. That I haven't succeeded doesn't necessarily mean much, but how likely do you think it is that Apple's product and engineering teams didn't try the same before deciding they needed to ship a whole new app about it?
If that's true, why does every mainstream music app do such a terrible job with classical musical?
Possible because they think something like "none of this sounds anywhere near as complicated as people are making it out to be."