Since you're the one making the claim:
Please put together some numbers of what it costs to work with an international payment processor, managing refunds, customer support options of any sort, managing multi-state and international sales tax revenue and accounting, an update and distribution platform, a CDN equivalent, an easy beta release mechanism, decent security and signing options, your own marketing website, software developer time or salary to build and integrate all of these things, etc. It's possibly more than 30%. Plus if every indie game ISV had to do that stuff that they may not really enjoy just to launch a game, they may not bother writing the game in the first place. This is all value added to the platform.
Which is why everyone has been cool with paying basically the same cut for literally every other platform as well.
They're just unwilling to participate in Capitalism as far as their platform is concerned by pre-emptively blocking off any competition. They want a dictatorship and they want you to pretend it's out of their benevolence.
I thought that capitalism meant that, if it’s their platform they set the rules, and should be allowed to decide what gets sold there and under what conditions.
If you want to sell anything in a physical shop or in Disney World, you have to deal with the conditions of the shop owner, too. It wouldn’t even surprise me if Disney took a cut on each ice cream sold in their theme parks (sellers might even prefer that over a fixed price contract as it moves part of the bad weather risk out of their hands)
The only reason to deviate from that here may be the sheer size of Apple’s platform. That may make them so powerful that their free reign over their store must be restricted (a similar thing has happened in some countries with big supermarket chains versus producers of goods. If Walmart were to decide to stop selling brand X as a negotiation tactic to get better conditions, a court could forbid that)
Imagine that half of the US was Disney World, wherein everything is dictated by Disney because they managed to get there under capitalism.
Capitalism is a great tool and all, but as all other tools, it doesn't solve every problem. In this scenario, it has stopped working inside Disney Nation/World.
It makes no sense for them up-root their entire OS and ecosystem just to switch to Vulkan. Microsoft has no interest either.