I know this is going to be a hot take especially on the lemmyverse, but that's not the fundamental problem.
The issue in question is: should a company that provides a product, one whose value proposition is focused on a cohesive ecosystem and experience, be forced to break down their walled garden to let people create a new app store or install apps in a way that's outside that companies vision for their own product.
My personal opinion is that it's a dumb fight for apple to take, because 99.9% of their users will never deviate from their app store. But I understand why they are fighting it. I'd fight it too. Huge companies that have made a fortune benefiting from the apple ecosystem have gotten so big they want to take even more and forgot how much value apples environment and user based provides them.