No, this shows a fundamental misunderstanding of how the market works.
Literally every other storefront competes with Steam on 'rates' very easily.
Anyone can sell Steamkeys directly from a games publisher, including the publisher themselves if you want to make sure that the entirety of the purchase price goes directly to the publisher. Or give a percentgae to charity with every purchase, as Humble does.
Steam does not make a penny from any sale not made directly through Steams storefront.
Conversely, MS - whose storefront you are championing as "competition" - is the sole distributor, supplier and vendor of all UWA keys. It is entirely impossible to create a UWA without using MS made tools, going through MS terms and conditions, and going through MS certification for every release.
The only party that unquestionably benefits from UWA is MS.
By using Steamworks, any software company can create, update, and sell products without ever paying Valve.
e:
Let's not pretend these exact points of comparison that work wholly against MSs favour haven't been brought up a hundred times in UWA topics now either.
Show me where I'm "championing" anything LOL. Not by any stretch of the imagination. I've described this as situation as nothing other than a cluster fuck. Let's get that straight.
Secondly, all of the other avenues for distribution, doesn't change the fact that good ole' fashioned Steam Is the dominant distribution method. a publisher using steamkeys is completely different from a publisher offering a storefront perks inexchange for the increased visibility storefronts provide.
Lastly, you need to separate your hatred for Microsoft from what my comment actually was. Not an exuse for MS' gaming efforts, rather an exploration as to why a 3rd party would consider making this venture.