Okay, I've had it with this nonsense.
Dear Apple,
Please build a sandboxed and neutered Third Party App Store capability into iOS so that Spotify, Epic, and other mouth breathing agitators who are only causing a worldwide stink because they have reached what is called The Law of Diminishing Returns will finally and truly shut their vacant minds and pie holes.
Spotify and Fortnite can't grow as fast or as big as they used to because they have reached Market Saturation. Anybody who was going to use the service and has heard about it would already be on the service by now. Spotify and Fortnite now have to go after people who have somehow not heard about them yet, or increase prices to show revenue growth to their mouth breathing toddlers on Wall Street.
Barring any new products or services, both of these loud mouths need to find new areas for growth, and so cost cutting is the first thing any company does to produce this.
Unfortunately, one of Spotify and Epic's largest costs, other than paying salaries to their developers, is the 15% service charge for being allowed on Apple's App Store. It's the same type of fee that credit card companies charge to use their trademark such as Visa, Mastercard, and AMEX, etc. Sure, there are only two mobile OSes of any merit, but that's not Apple or Google's fault that everyone else failed. Just as Microsoft was not a monopoly in the 1990s because Apple had a failing market strategy under the disaster that was Pepsi-boy.
Apple, you should just make a severely restricted and sandboxed Third Party App Store that you take 2% of all yearly revenues from each Third Party App Store owner (much larger than an individual 15% app sale cut, but humans are dumb and see 2 is smaller than 15). If you remember, A&W released a Third Pound burger back in the day to compete with the Quarter Pounder with Cheese at McDonald's. Americans thought 1/3 was smaller than 1/4. So, I'd say this is your best bet at winning the argument.
Once this is done, Spotify and Epic's arguments will be settled, you will be in compliance with the DMA, and you can charge a service fee of 2% Yearly total revenue in much the same way a licensor collects royalty payments.
However, they'll be back for more. They'll keep pushing the issue, but ignore them.
See, on Android, which supports multiple App Stores, the vast majority of users buy and download apps from the DEFAULT App Store the device comes with. This means that in Android land, over 90% of all sales are in the DEFAULT App Store for the device (Amazon, Google Pay, Samsung, etc).
Since all iPhones ship with the Apple App Store by default, what little money Spotify and Epic stand to make from this move is negligible.
You can then, as a conscientious and aware protector of consumer interest, can inform the user that Apple has no control over data collected by a Third Party App Store, that the Third Party App Store may have pornography, viruses, malware, and other filth not allowed in Apple's clean and pristine walls and that any and all issues arising from the installation of any and all apps from Third Parties is not covered the by the Manufacturer's Guarantee, the One Year Warranty as required by Federal Law.
Then wash your hands of it and let Spotify and Epic's third party App Store get overwhelmed by ShovelWare, MalWare, intrusive ads, and other lower brained experiences pushed by empty intellect marketing agencies.
Meanwhile, the rest of us will understand you tried to reason with them and their ilk, and yes they won in the end. But....MY HORSE! My kingdom for a horse.