Why not? People are generally always online these days and there is a lot of music out there, plenty to fill a phone many times over. Granted you might only have a few hours worth of tracks at any time but there is obviously at least one person (OP) who doesn't.
Not to mention the way they manage their library sounds incredibly desktop oriented. This removes the need to plugin the phone.
And then like Plex/jellyfin, or audiobookshelf, sounds like this let's you have a shared library across devices or people, even better!
I would say with all of these recommendations, you can probably look to find an AM4 motherboard and user ddr4 instead of ddr5 ram secondhand. If you play heavily modded Minecraft, ddr4 ram will be much more affordable to opt for 64 GB if you want to allocate 20-30gb and keep a lot free still. AM4 motherboards cover a large range of CPUs up to ryzen 5xxx I think. there's a lot of room for upgrades if you can only find one of the older CPUs. I jumped from a 2700x to a 3900x recently and it's been great
Edit: only just read your future proof comment. Older parts may not be the way to go then, since you're restricting upgrades to things which already exist Edit again: I thought about it some more and I think this tier of parts is actually future proof, in that it should do the things you said you're interested in doing into the foreseeable future