I have used Tune my Music to import into Spotify from Apple Music and I have realised that it didn't take into account what I already had in my Spotify account and therefore had a lot of duplication.
I decided that the best approach was to remove everything and start from scratch. I removed all songs on my Mac and now its showing as no songs in the songs tab, however its still showing most, if not all, of the artists in the artists tab - same for albums.
Additionally, a number of these are marked as "following". If I unfollow on the Mac, they stay there and don't go away. If I unfollow on my iPhone, it disappears, but that change is not reflected on the Mac.
I'm not sure what the issue is here, but my library is a mess and I want to give Spotify a chance but not sure how to resolve this!