IANAL and I cannot judge the legal merits of this case.

I did read Apple's response though and I found the argument not a compelling justification for their practices.

A big part of their response is to justify the need for the 30% as a mechanism to recoup costs. That sounds perfectly reasonable until you realize that Epic is not allowed to recoup its own costs for the higher App Store cost by increasing their product cost by 30%.

Instead it must take a loss on the product and charge the customer the same price as app stores that do not take as large a %. That makes little sense.