I created my first Spotify account in 2011 I'm pretty sure the ONLY way to authenticate was Facebook. There's no way I would have used Facebook rather than email.
Years later I realized how absurd this was, found out you can't unlink them, and just made a new account. Spent a couple of days transferring my playlists.
I've had a Spotify account for just as long and never had it linked with Facebook, purely because I didn't have Facebook at the time. I just log in with id and password.
