Would you disagree if this was a startup whom had built an app store over a decade and was getting violated?
I am not a fan of jagurnaut tech companies but the rules are the rules. They built it and from what I can see (I am an IOS developer) the payment system is indeed in violation.
The guidelines clearly say that apple payment system MUST be used. It doesn't matter if you are Spotify or an indie game dev.
is 30% steep? absolutely! But hey if it was my business I would love it its a great margin - so would you.
Bottom line is Spotify is in violation and they don't want to pay the 30% which Is understandable but Apple will not budge because they don't half too.
TLDR; "Apple to Spotify: Kiss my Ass".