Here's how I know the algos are trash: I use Apple Music. I've uploaded probably 100gb of archived music, labeled and tagged on top of whatever I've "added" to my streaming library. They should be able to know EVERYTHING about what I would be interested. It is obvious to everyone, instantly, that I am a metalhead.
They have essentially nothing that I would ever listen to on the "browse" tab, auto complete suggestions I would never want and "For You" suggests albums I already own.