Have you tried to load UWP apps on a machine with less memory? I believe that part of what's going on there is framework-level shared, memory-pressure reclaimable caching.
On a machine that doesn't have as much memory, the frameworks don't "use" as much memory. (I would note that Windows IoT Core has a minimum spec of 256MB of RAM, and runs [headless] UWP apps just fine! Which in turn goes up to only 512MB RAM for GUI UWP apps.)
Really, it's better to not think of reclaimable memory as being "in use" at all. It's just like memory that the OS kernel is using for disk-page caching; it's different in kind to "reserved" memory, in that it can all be discarded at a moment's notice if another app actually tries to malloc(2) that memory for its stack/heap.
I think the more amicable solution here is to just have higher standards. I might not have given up on Windows (and UWP) if it didn't have such a big overhead. My Windows PC would idle using 3 or 4 gigs of memory: my Linux box struggles to break 1.