1. This presumes Spotify will still be in business in the next 10, 30, 50+ years.

2. This presumes 100% of the music collection is on Spotify. Personally speaking, 60%~ of the music I listen to ISN'T on Spotify.

3. This presumes music is only desired to be listened to when an available internet connection is available.

Having to shuffle my media collections around whenever a third party went out of business or pivoted was such a massive headache that it was the inspiration for just managing my own media collections locally.

This is just my own personal perspective on the matter but one could do that until the Spotify domain is gone. The mp3's will remain provided they have a habit of keeping their software backed up. I have CD's, DVD's and music files going back as far as such things existed and no internet connection is required for any of it.

Despite iTunes fans bashing me since iTunes inception the simple file structure

    Artist
        Album
    Artist
        Album
    Game OST
        Game Name
    Film OST
        Film Name

works just fine.

With WinAmp's quick jump it was a blast to navigate.

(just checked - my mp3 folder has 6231 files)