Apple is under no obligation to make someone’s ideal business model feasible. Just like if you want to post content on Facebook, or if you want to sell through Stripe, or you want to deliver groceries on Instacart, or you want to have a business in the USA - you have to follow the rules created by the owners of the platform you stand on, or find/start a new platform. This is a fundamental aspect of social life, not some corporate profit-seeking BS from Apple.
No one is making DHH do an email app. No one is forcing him to charge $99. If Apple is so big and bad, then maybe he should be working on a new mobile phone platform instead of another email app. Complaints about injustice without alternatives hold little weight.
Finally, if this was something society actually needed, I think I’d feel differently. If this fight was over an app that was critical to survival or civil liberty or something, it would mean something different for Apple to reject it. But it’s not something we need. It’s not important or critical in any way. It’s a new email app. Forgive me for not busting out a bigger violin for someone who has already released multiple profitable software products and is now upset that an even richer entity won’t let them have their exact way.