EGS is really the only thing remotely close to what Steam does, though.

GOG will always be an afterthought as long as they have their DRM-free policy in place. They're super cool, but they're a niche and will never grow beyond that without losing what makes them cool.

Origin (or whatever EA's calling their store now) gave up pursuing third-party sales years ago. They still do it, but they clearly have no interest in actually making a go of becoming an actual competitor to Steam.

The Windows Store is terrible for a number of different reasons, even if it's better than Microsoft's previous attempts at getting into this space (coughGWFLcough). EGS is more likely to overtake Steam than Windows Store is to even rival EGS.

Uplay (or, again, whatever Ubisoft is calling their store these days) is like Origin - I don't even know for sure if Ubi is doing third-party sales, but if so, it's very much an afterthought for them.

And then everyone else just sells Steam keys. They're not in the same market as the others, so don't really fit into this conversation. If you're 100% reliant on the store you're "competing" with, you're not competing with them.