I disagree with your entire take. Namely because you assume they can do whatever they want.
A mall owner can't dictate how it's residents receive money.* Nor would it be wise of them to take a share of their commercial resident's sales.*
I'm not arguing on legality. I'm arguing based on social norms (not ethics either).
Apple is extreme social behavior of a corporation. There are multiple situations where Apple copied something another app developer made.
I doubt Epic will win but...it may open up the conversation and maybe finally encourage other developers to push back on Apple, so that a more socially acceptable structure is within the App Store (and it's ecosystem).
If this doesn't cause Apple to reform, the next escalation is clearly inciting a frenzy to push the Govt to execute judgement with the antitrust laws. Even if they're outdated, the case is clear. Apple hasn't just been a bad actor once or twice but numerous instances. If Epic does this with their current case, I'm uncertain that they'll achieve their desired outcome because their limited situation doesn't seem as clear cut.
* - If the contract says this...it's still not socially fair. Land is vast...the phone ecosystem is not. Which means a mall owner will meet a lot of competition to push them to either change or they'll go out of business due to undue hardship put on the commercial tenants.