Witcher 3 is nowhere near one of the most demanding games.
The game was 900p on X1 and 1080p on PS4. The dynamic resolution of the Xbox One X version displays between 1800p and native 4k.
Also the game came out less than two years after PS4 and X1 launch. The game would look and run vastly superior if developed today.
With that being said, I don't see why MW wouldn't run on Switch. 720p 30 FPS should be possible. Biggest issue would be HDD space though. 100GB at the very very least.