Spotify is just the company who complained and have enough lawyers to understand anticompetitive law, but any ruling on that will benefit all app editors.
And frankly, most Apple users will keep paying the 30% tax anyway, it's not enough to loose the convenience.
Forbiding truthful, legal speech on your platform is allowed, but not if preventing it is anti-business and anti-competition.
I thought people on a website called _hacker_ news would be supportive of a ruling allowing small app creators alternative payment system?