I mean, most of Steam's advantages at this point stem from being an established platform. It has well-developed social features, it has achievements, it has the workshop, it has the market...
... but if there's one company that can go toe-to-toe with Valve, it's Epic. Their launcher already has a massive user base thanks to Fortnite, and they take smaller cuts from purchases than Valve, so companies have a pretty good incentive to use their store over Valve's.
If Epic can start getting must-have exclusive games on their platform- and they're damn capable of this- then Valve's going to have to step it up. (Which basically means they're in trouble, because Valve isn't known for stepping it up.)