> platform development

It's almost 100% platform development. The iPhone is a walled-garden game platform and Apple treats it like one.

To answer your question, it probably isn't sensible to expect Apple to charge a drastically different platform fee in its game store compared to what is charged for other walled-garden game platforms and stores like the Nintendo eShop.

It may be worth noting that Amazon's Luna game service can work on the iPhone in a web browser, so game streaming isn't exactly an Apple-enforced monopoly.