Exclusivity arrangements certainly seem like potential trust issues, but Steam is a de facto monopoly, as is Amazon, and NetFlix is the clear leader in it's domain.
For example, NetFlix France is a joke, you couldn't watch any netflix shows because they're not available, they sublicensed to canal (the main paid TV service) with exclusively and are left unable to serve their own TV shows.
The Epic Store (and Steam) are global. That's more than 200 jurisdictions with different rules on anti competitive behavior. They are preventing competition globally and systematically, this has to be breaking some rules somewhere.
Either that or there is some (justifiable) brand confusion, as there are brands/companies spelled like that: "iPhone", "eBay", "FedEx", "DreamWorks", "HarperCollins", etc.
That said, the DoJ has in more recent times taken the opinion that anything that lowers prices for consumers is implicitly good and anything that raises prices is implicitly bad and used this as the basis for leveraging antitrust complaints against companies that were not in fact the monopoly. In particular I'm thinking about how the monopoly player in ebooks (Amazon) successfully convinced the DoJ to sue the brand new entrant (Apple) because what Apple was doing was causing problems for Amazon's strategy of artificially pricing books lower than they should be in a fair market (even though what Amazon was doing is literally a monopolistic tactic intended to cement a monopoly and prevent anyone from competing, which leads to raising prices down the road once you're sure the competition is gone, i.e. Amazon successfully convinced the DoJ to use antitrust laws to help Amazon cement their monopoly). But since Epic isn't raising prices for games, that doesn't really apply here.