I wish macOS had a really solid Winamp/foobar2000 music player. Most now are all about managing a library (no thanks, I have a filesystem for that!) or integrating with cloud services.
I appreciate this perspective but I loathe using the filesystem to manage a music library. If a music player doesn't have a well designed and highly functional music library I most likely won't use it. Most are half-baked though, unfortunately.
You could try DeaDBeeF. It's Linux first but there are Mac OS builds. I've tried it, may be a little buggy on Macs but could be worth a check to see if it works for you.
I'm curious what your objection for organizing music in the filesystem is. Even music players packed with library management features need the files to exist somewhere, so organizing things intuitively on the filesystem seems a good starting point. The alternative, I guess, would be importing them into some non-navigable structure like a binary blob? I would think maintaining a persistent index of all the metadata is all you need beyond the individual files.
I keep my files well organized on disk, but I am also particular about how names are both shown and sorted, and rely on careful and comprehensive tagging instead. For example, I will not name folders "National, The" or "Beatles, The", or "Petty, Tom", but when I'm looking at my music I want The National to be filed under N, the Beatles under B, and Tom Petty under P like I would arrange on physical shelves. The compromise is that all the "Thes" land together in the filesystem, but are shown the way I like them when I go to play music.
I also want albums to be sorted by (original) release year but don't want to put the year in the folder or file names. Similarly, I want to be able to search, and with classical music it is nice to be able to show by composer or conductor or soloist, etc. Tagging and a robust music library make these things easy. Using the file system does not.
I always kept mine under {first letter}/{artist}/{album}/ Where "first letter" in, say, "the Beatles" would be "B", not "T". I had a separate folder where artists that started with a digit would go. Another folder for the occasional glyph. e.g. µ-Ziq.
