I am adamant that the change occurs at Win 10 1607, with Win 10 1511 being the last semi usable build. (I say semi because Windows XP is better than anything after it).
The reason I keep bringing it up is that any Microsoft engineer who might take an interest should hopefully look at what happened specifically to the graphics stack on Win 10 1607.
While the very first builds of Windows 10 (1507 and 1511) aren't especially relevant to everyday use and aren't a great workaround anymore due to lack of modern software and hardware compatibility, they stick in my mind as a significant point of change in the Windows graphics stack.
This is not to contradict that DX 12 is part of the issue. While Win 10 1507 and 1511 include DX 12, perhaps they are not fully activated or utilized in how the screen is rendered.
@reaganry @Sunspark I use both Windows 10 2015 LTSB (1507) and Windows 8.1 and they are both rendered similarly in my personal experience. Same feel to the eyes and brain and also subjective image properties.