I can relate to both sides of this fight, but to lend my POV on Apple's stance, they have a valid argument.

When you sign the developer agreement and submit an app to the App Store, you are entering into a contract to make concessions to Apple's business model, and Epic clearly violated these T&Cs.

If Epic truly wanted to institute change in App Store policies in order to maximize their profits from Fortnite, they would have first engaged Apple to initiate the discussion and work towards an amicable solution, which Apple would likely flat out deny. It's at this point that Epic could have used its substantial presence in the industry to rally the developers, the press, and its own user base to stand up to Apple policies and effect that change.

As it stands, their decision to wait for their assured dismissal from the App Store to pursue litigation and position themselves as trying to "stand up for indie developers" comes off as insincere and primarily seeking publicity based on Apple's action in simply abiding by its own long established policies.

Note: While I am primarily a Mac user in my personal life, I tend to be very critical of Apple's business practices in general, and while I have my own negative opinions about Fortnite's transactional model, I try to be unbiased in my response to their actions and subsequent behavior.