I’ve honestly never understood people who feel the need to “replace” Spotify. … Spotify has never made sense for my use-case.

I don’t know how to say this, but…you have extremely uncommon use-cases:

…during those times, my phone is either fully turned off (so I’ll use an MP3 player), or it’s in Airplane Mode.

Many people listen to music on stereos and don’t necessarily want a device plugged in, so

I just download the music I like to my device and listen to it via VLC.

either doesn’t work or is substantially less convenient than e.g. casting from a phone.

Not hating on your setup at all, but it’s very niche, in my experience.