Not really.You're confusing platforms with marketplaces. Can you run macOS apps on Windows? Can you put a Honda cd-player into a Toyota? No, but that has nothing to do with how apps or cars are sold, and has to do with software and hardware compatibility, interfaces, etc.
The App Store on iOS is the same idea as a PlayStation being able to only play PlayStation games. It’s a closed system. There’s no “anti trust” nor “monopoly” here.
As for prices, that’s up to the developers. Since the developer sell their apps directly to consumers, there’s no anti-trust imo.
In the traditional retailer concept, retailers buy stuff from the producers, and then they compete with each other by re selling the product to consumers. Consumers don’t interact directly with producers.
But what if the producer themselves can sell their stuff directly to consumers? That’s what the App Store did, allowing software developers to sell apps digitally directly to consumers. So the traditional concept of “competition” and “monopoly” no longer applies here. The software developers are pricing their own products and selling them directly to consumers via the App Store. Why do you want a “competitor middle-men” here when you are already dealing directly with the software developer? Why should the software developer be competing with him/herself?