You absolutely have no clue what you are talking about.
Take attached images. The full image is 3840x2880. The image with #1 is cropped from the source and is still around 1200x1200 pixels and 350kb. Image #2 is a screenshot of the source and then cropped, same as image #1 was. 300x300 pixels and 23kb. Get the idea?
Now look at the images he is posting here. The image he is screenshotting doesn't fill his display, so again it is even lower quality.
Apple doesn't have some magic sauce that makes screenshots keep a higher resolution.