I think you undersell how feature rich steam is for both users and developers.
They offer community forums, reviews, mods through workshop, cloud saves, automatic controller support, openish vr ecosystem (epic cant even do vr, if you buy a vr game you likely need to use steamvr anyway), broad payment and currency options, regional pricing and guidelines, remote play, and more I’m sure.
This is much more feature rich than even console platforms, so I think the 30% fee is justified.
And they do this all without really locking down their ecosystem.