I have no sympathy for Apple or Google, they have brought it on themselves. But S Korea’s proposed law is not the way to do it.
It does not solve the real problem, lack of competition due to abuse of their enforced monopoly. In Apple’s case as the only store in town and in Google’s by making it difficult to get from any store but theirs.
For paid-for apps they still get to set the cut they take. What’s to stop them charging 25% if you use another payment system 30% if you use their payment system.
For in App purchase why would they have the app in their store? Why should they if they are not going to get any revenue? Which would be the case for Epic’s game.
The fix is to remove the restrictions to competition, by allowing users to easily purchase/download apps from other stores or direct from the app publisher.