AAA/published developers will use the Microsoft and Sony and Nintendo APIs.
A/funded indie developers will use Steam.
Mobile developers use Apple and Google services.
The Unreal Engine can be very CPU intensive for server physics, so if you want hosted game servers that are authoritative, you’ll have to pay a fair bit in fixed cost.
And if all you want is matchmaking and leaderboards, then you’re likely to go with Steam, or perhaps Xbox Live for Windows if you go the Universal Windows route.
How, exactly, will EPIC make money on building this? Who are the developer/customers that will actually pay enough for it to cover both hosting, operations, and the significant development effort?
Maybe they exist – but I have yet to see a reasonable market sizing for this.