These are the same pedantic assumptions made back when the Windows 8 store first came out, that we'd all be locked into using 'metro' apps with no backwards compatibility, which as an early adopter of the dev preview I can tell you was never the case -- the store was just an effort to give users what they thought they wanted.
Hell, these arguments go back even further.. I remember how frantic everyone was about Windows Vista, just because MS had let people get too comfortable on XP. Even XP caused huge upsets over just being able to run more capable software. And from the switch from 3.x to 95, or the switch from MS-DOS to Windows..
But in spite of all of this, I still see many enterprises still managing to run programs that are basically modern front-ends for ancient DB software from the 80s (all of Ohio's Unified Accounting Network still basically runs on top of MS Fox, for example) on modern systems running Windows 10.
The key to MS's ubiquity and success in the PC market is it's compatibility. Over twenty years using their operating systems, and practically nothing in my massive collection of ancient hardware, software/games, and peripherals doesn't work practically 'out-of-the-box' on Windows 10 -- and it's getting easier with every new iteration.
The store does nothing to change this, and if anything just adds to the experience. Epic Games can chose wherever and however they like to distribute their wares, and MS has done nothing to affect this. The only real complaint is that end users may just end up preferring UWP so much that it becomes as ubiquitous for Windows/xbox as the stores are in iOS/Android, so much so that devs will be forced to offer their software on MS's store just to be able to compete -- but we all know that won't be the case. x]