While I am not a huge fan of Apple's walled garden approach, and I think a 30% cut on all digital sales is too much, they appear to be in the right here. I wouldn't be surprised if they win the main suit, but the countersuit is thrown out.
In comparison, Valve also takes a 30% cut but they do a good job of trying to advertise the products of all of their customers, big and small, massive umbrella publisher or indie dev, equitably and fairly. They provide tools for devs and publishers to better inform customers. They give them a place to make as elaborate a storefront as they want. They maintain community centers such as forums for these companies. And more. In short, I think Valve earns their 30% by basically alleviating much of the effort and stress of advertising and promotion from the shoulders of their customers. Apple doesn't do that. Unless your app / game / whatever happens to hit it big from no fault of their own, they don't care.
I think Epic is being hypocritical. They influence competition and gain market share in the digital games market not by offering a quality product (Epic Games Store is anything but quality, being merely an echo of a launcher), but rather by throwing around figurative bags of money from their multi-billion-dollar company's warchest to secure exclusives and give away old games. So I honestly don't care if they lose or how much they lose from it. If Fortnite and all Unreal Engine games disappear from the Apple Store and Google Play, oh well. Poetic justice in my opinion.