Geez o flip!
Talk to Evens about how long a bike change can take. Planned or not, 10 seconds lost on a bike change is bogus even in the absolute best situation. 30 seconds is optimistic
Yes, folks tried it a few times and gave up on it. I mean it so 1990's dude
Anyone want to try and claim one TDF victory on having a light bike? Anyone
Fact is even today, many if not most tour bikes are over 6.8k. It just does not really matter much when looking at the overall picture. Fit, comfort and reliability count more. Why you may ask, it's the rider not the bike. More gains are to be made by making the rider perform better, with fit and comfort by reducing rider fatigue. Mechanical failure, in a machine with poor reliability, will set you back big time.
On an uphill TT, like the Mount Washington hill climb, provided the bike is stiff and reliable an advantage can certainly be gained. These limited applications are not the norm however. That race, all uphill, has no 6.8 and riders on bikes, purpose built in the 12lb range, have been seen on the podium. (Some of whom were also taking advantage of EPO BTW. So did the light bike win that race?)
Believe what you want. If you want think that every gram counts much in a stage race, well maybe it will, but I think the question will come down more to sports psychology then the physics