I think you're mixing up analogies. The app developer is analogous to a business, and Apple is analogous to Walmart, Target, Amazon, etc.
You're correct though in that no one would have to force a business to sell through Walmart, Target, or Amazon because that business would be able to choose where it sells it products and can extract favorable terms from one retailer to use it against another retailer. If the business doesn't like Walmart's terms, it can go to Target. Don't like Target's terms either? It can go to Costco, Amazon, or one of the many other retailers. It can even launch its own website and sell directly to the consumer.
Can't do that with Apple though as they're the only game in town.
That is anti-competitive. The EU's Digital Markets Act aims to fix that.
You might be able to have more than one app store.
www.theverge.com
Other countries such as South Korea and India will eventually follow
Apple is to again be investigated by South Korea's telecommunications regulator, alongside Google and One Store, over suspected violations of...
www.macrumors.com
The Competition Commission of India (CCI) is reportedly nearing the conclusion of its antitrust investigation into App Store, and is expected to conclude that Apple must open it up to rival alternatives.
appleinsider.com