The solution to duopoly power is to introduce more parties. Breaking up the App Store still leaves the duopoly power around. And I can certainly see this going to a $300 Apple developer fee and $500 XCode license to make up for the 30%. And you (developer) having to deal with individual line items for CDN, support, transaction and other items.
you dont need to break up anything. If you want to develop a game/app for windwos you have multiple places to sell this product.
If you want to develop ot Xbox/PlayStation, you have multiple platforms to sell from.
if you want yo develop to Android, you have multiple places to sell it.
If you want to develop an iOS app, you need to use
ONLY APPLE APP STORE
a developed iOS app can't be sold on android. it must be a new app
a developed Xbox game can't be sold on PlayStation, it must be made a new one for it.
Xbox doesn't stop PlayStation games from being sold on Xbox store, it's a different OS and architecture.
Android doesn't stop apps from being sold on iOS App Store, they are incompatible systems on a technical level.
iOS stopps apps from being sold anywhere else outside their store. the prevent any alternative payment options.
apple could even force third party payments be displayed next to iOS In-app purchase function, just as they force every app to have Apple login alongside Facebook and Twitter logins etc.
Apple could even vet and sign every app as now but allow the exact same app be sold on competing stores, or even on the developer's website. And if an app breaks apple's rules on the store, it will lose its verification and not be possible to install, just as you can't install a downloaded iOS app today that doesn't have apple's signature or your Apple ID connected to it.
this allow you to keep all the safety but compete on services