Richard Stallman wrote a quick page on the shady things Spotify does (3 minute read not counting the linked articles). Although only loosely related to what you asked for. According to the info I found online, Discover Weekly should be safe from the kinds of sponsorships you talk about (the whole article takes about 8-15 minutes to read, but I quoted the important part below).

A representative for Spotify tells Vox that the user experience of Discover Weekly will not change — e.g., Nike can’t buy the playlist for the week and serve everyone a Frank Ocean song — and reiterates, “Discover Weekly is, and will remain, a powerful means of artists winning new fans.