To each his or her own. I, for one, would notice the weight difference. Case in point:
The other night, I packed up my gym
bag and took it downstairs in preparation for going to the gym. As I got downstairs, it occurred to me that something didn't feel right - the bag felt much lighter than it should - and sure enough, I had forgotten to pack the plastic flip-flops I wear in the locker room. Out of curiosity, I weighed them, and they came in right around a pound, so not much more than the difference between the M2 Air and the 14" Pro. This was in a bag with gym clothes, running shoes, socks, weighing 5 lbs or so, yet the 1 lb differential was immediately noticeable.
Since I quickly noticed the difference in the gym bag's weight while descending just one flight of
stairs, I think the difference in computer weight would be quite noticeable to me as well.