Why you say is reasonable but how do you see a realistic implementation? Currently, the economic model of App Store is based on taking a percentage of the revenue. This model is simple, transparent and it has a beneficial side effect of encouraging new developers. You only pay if you are successful, which makes it cheap to try and less devastating to fail (compare it to "traditional" models where you have to pay a listing and distribution fee without knowing if your product will be successful).
Simply lowering the fee won't work since Epic will still complain that they are giving away profits from their "digital goods". They will still continue their crusade even if Apple lowered the fee to 5% for them... as they could still make more money by using their own payment system. Removing "tax" from digital goods won't do any good — because then everyone will release "free" apps with in-app purchases. Negotiating terms with each dev individually? How would that work? Who would regulate it? Who would pay for the army of lawyers need to maintain them? Epic's argument is already based on the notion that Apple's demand of a profit share is unlawful. If they win this round, good luck getting any money from them. No matter how I look at it, the end result is that the basic economic model of the App Store is breaking down. This means higher costs for small devs, this means less innovation, this means crappier apps.
What is really funny is that Epic and their buddies are claiming to do all this "for the little guy", because 30% is apparently too much to bear for a small dev. Well, Apple has addressed it — the small dev now only pays 15% (Epic themselves charges 12% but offers less service). So Epic should be happy, right? Nope, they are not happy, because they are leaving $$$ on the table.