Is this not like complaining that Walmart dominates its suppliers in Walmart stores? They also sell their own brands plus demand suppliers offer and price exactly what Walmart wants.
In the case with Apple Music vs Spotify, Spotify is not only at a disadvantage of API availability, but also how the rules are not applied for Apple's own apps (marketing push notifications come to mind). On top of that, it is more difficult to complete on price as you are coughing up 30% for any IAP (which you have to use Apple's IAP APIs to begin with). So spotify either charges an extra 30% to cover the fees or eats the 30% to remain price competitive.
Like, if you have a product, there's the retail price, and there's the wholesale price that Walmart pays you. There's a spread that you pay going through Walmart that they don't have to pay for their own products.
Now, it's definitely not 30%, but its there. I think the numbers change how onerous the splits feel, but the mechanics look similar.
Supermarkets are frequently subject to antitrust action in Europe.
In fairness, "almost everyone" shops at Target/Walmart. That's why everyone's so desperate to get the buyers at Target and Walmart to do business with them. It's worse actually, because you can get on App Store or Google Play, and still not do very well. Whereas if you get space at Target you're set.