And there is nothing stopping Epic from releasing Fortnite on the iPhone (in-fact it was there for years).
The rules could be unfair[1] but this issue is just Epic not wanting to follow the rules to make some more money.
[1] We can discuss what a fair price/percentage should be. Arguably the market and Apple customers have decided 30% is fair, but we can discuss. Meanwhile, side-loading or not charging would make my iPhone experience worse.
My conversation with you was entirely about "the iPhone being a general purpose computer".
It seems we have both settled that either an iPhone is not general purpose, or all consoles, TVs or IOT devices with downloadable content are general purpose devices.
If you'd like we can now start discussing if the price Apple charges is fair.
I've already stated, the market decides to buy iPhones understanding (even appreciating) that the user cannot side-load non-Apple approved apps (other than through a less trusted channel i.e. the browser). As such the market through demand, has decided there is a niche ecosystem where 30% fees for in app purchases are appropriate and fair.
All of those platforms have stores, all of them allow digital downloads of software that executes, all of those have browsers.
What makes the iPhone "general purpose" where the others are not?