What strikes me as a bit odd with relation to specifically competitors to the Valve client (essentially a game library and store rolled together), the competitors that come to mind are...
* EA/Origin
* Epic
* Ubisoft
EA and Ubisoft are only selling games they publish, IIRC. Epic sells games from other publishers, but always gives Fortnite preferential treatment (and has the Unreal Editor in its own tab in the client, or did last I paid attention).
Valve is still by a large margin the only one that comes to mind that feels as close to a neutral store/library as you can find (even when they released Artifact and Alyx, neither of those were permanently pinned to the top like Fortnite is in the Epic store). Of course, developers can still buy preferential treatment, but it at least feels like you're competing with other developers and not "the house".
I'm not making an argument that Valve's being anti-competitive here, just it's surprising to me how hard these competitors -aren't- trying to be a real competitor. I expect due to internal pressures from their respective game publishing branches.