I have a carefully curated 70 GB music collection that I've been working on since the late 90s. I sync it to my iPhone in its entirety, bc I have the room. Other ipads and laptops have a much smaller (like 3 GB) collection just to have on hand if needed, with selected bangers. I have custom playlists that I like to use, too, so I am a big user of iTunes/Music for this, and can confirm its definitely working less well year after year.
I also do streaming—highly recommend Triode, fantastic internet radio app, and I'm also a big fan of Radio Paradise, which is on Triode, or on its own app. Both are free.
Otherwise I have free Spotify, just to access other people's playlists, and I pay for basic Pandora bc I have been using that for almost 20 years.
I definitely do more streaming now than I used to—I get why younger people don't collect music. That said, it pays off—I have lots of tracks that don't really exist elsewhere, and there's a real pleasure in being able to make custom mixes where you sculpt the pauses between tracks by editing them, and making in-between tracks that are audio from movies, TV, or elsewhere. You can't do that with streaming.
I would actually love Apple to STOP syncing files with Music, and make music an app that just works with Apple Music...if they then opened it up so other apps can sync with iOS devices. Basically I'm saying if they aren't going to make it work well, they should open it up so other apps can take over managing my music.