For a mountain stage bike, there may be some advantage in using lighter wheels and transferring the weight to ballast on the frame.
I am surprised that metal weights are added to the crankset: a rotating part, rather than, say the waterbottle holders.
I appreciate the idea of lighter bikes for lighter riders. In pro racing this may not be do-able but for everyone else, it should be quite normal. I dont see why, as a 140lbs (64kg) lightweight, why should I have to buy bikes rated for 300lbs riders.