Just FYI, the screen brightness of the 14" is theoretically 3x as much... I use an an app called Vivid which doubles it to 1000 nits. This is pretty killer functionality to have for my use case as I like to work outside.
Yeah out of the box it will only crank to 1600 nits for HDR content.
If you compare vs. the Air screen without viewing HDR content they both top out at 500 nits, which is why some people are claiming they can't tell the difference.
If you view HDR (either photos or videos) the difference is huge.