Yeah, I play in 4k, and get shadowplay to output at 1080p from the 4k original, which means its downsampled. This gives a better quality 1080p vid, than recording in 1080p to start with for reasons i don't completely understand.
Downsampling is also used by people with very high horsepower computers, to give a better image in VR headsets.
The raw shadowplay footage looks much better, first win photos has degraded it (although i am very impressed by how little), then youtube does its butchering. At some point i'll upload a vid in 4k to youtube, to see what its like.