If I want a guard dog, I'll buy a Dober, certainly not a poodle. Form follows function. Period.
Feeding, proper training and exercising the Dober will get get you one lean mean sonafabitch watching your front gates. No, it wont be bitchingly heavy as a St Bernard that you can hardly carry which by the way you shouldn't be doing with a Dober. But if you want something to cuddle and hug, of course the poodle or that pudgy face Pekinese is a better bet.
Likewise if you buy a mountain bike to huck and bash, why would you want to pursue a sub 5kg holy grail? Trimming down unnecessary weight and using high strength to weight ratio component is common sense, akin to exercising your Dober to keep it from being overweight and sluggish. But if at the onset, it is already about building something that looks like a mtb from far but fails in performance relative to the intended purpose...that's utter stupidity. Oh yeah, and dont go ride in the backyard to justify "Hey, its light and off road worthy"
Just had to get this off today after reading a number of "how do I save weight on my already acutely anemic bike" postings elsewhere.
P.S. Regarding whether you will shave of 0.0001 microgram by sanding your spokes by a half nanometer isn't gonna get you far. Try some hack squats with free weight, Besides 2 finger spoke sanding is sooooooooo ghey...