You are missing the fact that epic is not a payment provider. So if they dont pay apple the 30%, they will have to pay stripe or adyen or any other psp. Most of those ask 0.25$ + 2% per transaction. For a fortnite skin of 0,99 or even whole apps that cost 0,99 that 30% is lower than the costs of other psp’s. And apple provides a lot more than just payments for that 30%. They handle disputes and refunds etc. and the handle all the money exchanges with sales is other countries etc