I carry my rMBP when I go shopping for the whole day with my wife, and don't feel tired too. The 2 KG weight is still very bearable to me, but not so much for my previous cMBP at 2.5 KG.

Agreed. After using the rMBP, the MBA's screen will look like a defected screen.

Can you help to check whether your display is a Samsung or LG display?

You need to open the 'Terminal' App, then Run the command in a terminal window to see if you have LG or Samsung: ioreg -lw0 | grep \"EDID\" | sed "/[^<]*</s///" | xxd -p -r | strings -6

Do let us know.
Cheers!