App store owners are compensated fairly by the 30% fee they charge as commission on sales. But the Fortnite case is not about sales. It is about the re-supply of virtual currency for use within a game. The customer is already established. There is no new selling or marketing or delivery required of the app store owner.
To recognise the differences between product sales vs ongoing consumable resupply, such as virtual currency, app store vendors should do what physical world vendors do and charge different fees that are commensurate with the value add.
Retailers charge 30-50% markup to cover the overheads of rent and sales staff. What Apple does with the app store is similar, and so their 30% fee is in step.
Forex dealers and banks charge 3% - 18% for financial transactions such as currency exchange and credit card financing. Given that Apple isn't even providing financing for Fortnite's virtual currency, a fee in the order of 5 - 10% would be reasonable in this case.
What's at stake here should not be the all or nothing duel that Apple has initiated by banning Fortnite from the App store. Apple should just evolve, and introduce a second tier charge for consumables.
Would it make sense for Walmart to charge one price (say $100) for every item it sells in every one of its stores? Of course not. Walmart and every other real world retailer charges different prices for different things, depending on how much value they add. Apple should do the same.