They have been great for what I use them for, occasion niche discoveries, but I'm not sure they replace Spotify for the "hop in my car and my favorite mainstream hits begin playing without having to think too hard about it" use case.

Oh yeah, it's not for that at all. I only listen to albums, so I don't need that. Heard people using listenbrainz recs for similar things

Isn't that what FM radio is for?