Apple knows they can end businesses with the click of a finger. That's what they tried to do by ending the dev license for Unreal Engine. And Apple wants everybody to know that they know. I'm almost certain that the Unreal Dev license revocation is a result of a similar email chain as what happened to Kindle - https://www.macrumors.com/2020/07/31/emails-apple-blocked-ki... - execs just thinking of a way to punish the company.
This, for me, is the biggest monopoly argument. Too much business success is hinged on Apple being happy, and they start to abuse this power more and more by tightening (the interpretation of) App Store rules like requiring in-app purchases etc.
IMO Epic is not the best company to challenge Apple in all this, but in American judicial system Epic may be one of the very few companies that can afford this lawsuit.