I don't think your first statement is actually true. Historically, the US has found that companies that act in a way to favor themselves over competitors is a p

I don't think your first statement is actually true. Historically, the US has found that companies that act in a way to favor themselves over competitors is a problem. Microsoft bundling its own web browser at the expense of Netscape, to name one semi-relevant example. So Spotify claims that Apple favors Apple Music over Spotify in an anti-competitive way, and that they control 100% of "the iOS market," making such favor relevant. Apple's argument will be basically the one you make: "our playground, our rules," and that they have made APIs available for Spotify to do all of the things Apple Music does. Which is true, but only very, very, very recently. Apple hopes that will reduce Spotify's argument to a monetary squabble over the 30/15% share. And that might work. But it's not nothing, and it's entirely possible for a company to exercise in anti-competitive behavior in their own marketplace, running afoul of anti-trust laws.