Content platforms always compete on availability of content. Steam did the exact same thing early on with Half Life. Look at what's happening in the streaming video space. Look at console gaming.
Ultimately, people aren't making Steam accounts because of the Steam workshop or Steam forums or Steam chat or what have you—they're making Steam accounts because there's a game on Steam that they want to play.
If Epic's store had better features but the same games, existing Steam users would still continue to use Steam, because that's where their existing game libraries are. The only way Epic could compete on features alone is if it were possible to migrate Steam purchases to the Epic Store. Since Valve will never let that happen, Epic has to entice users with exclusive games.
And that could be great for everyone—if it caused games to be made that would otherwise never get developed. Consider how much great content the video streaming wars have produced. As annoying as it is to switch between subscriptions, I'd say TV viewers are winning right now.
The problem, of course, is that Epic isn't developing original content—they're paying for existing content to be removed from Steam. My great hope is that this will change in time. Original games take several years to develop, so if any are under way, we wouldn't have heard about them yet. In the meantime, we're getting PC ports of Journey and Detroit, so that's pretty neat!