Why does Epic get the privilege to force me to buy things through their store?
Apple has said as much for the main developer account in the past.
It is highly unlikely Epic would publish anything in the App Store, however, even ignoring the bad blood.
Part of operating an App Marketplace is that you are agreeing to the EU rules which include a core technology fee. So even an app with no in-app purchasing on the Apple App Store would cost them a substantial amount to publish.
Apple overplayed their anti-competitive card, so now they'll be permanently scrutinized.