what you said makes sense to a point. although 25% of body weight is something I could only do when I was young. The body weight excess over BMI is interesting. When I was a competitive weight lifter in college I found out that when you gain weigh you also gain strength. It seems odd, but if you start eating a lot and go up to another weight class suddenly and surprisingly you can lift significantly more. So for some unexplained reason adding bulk automatically adds to strength. This may not apply to people not constantly working out with weights however. Also, I might mention, BMI is a poor measure for people with higher than average muscle mass. Muscle is heavy and if you rely on BMI for calculating body fat it will be wrong for weight lifters and body builders.

I have thought a lot about, and read a little about, exercise physiology, energy, nutrition and human performance and there are a lot of myths perpetrated by even experienced coaches. At the same time there are so many factors in backpacking and backpackers it is difficult at best to make any hard and fast rules about the energy expended, strength and endurance. Weight, distance, trail conditions, weather, conditioning and elevation gain just to mention a few.
Always interesting nevertheless.