That's true. However, by far the most common explanation for "I started eating less, counting calories, and I gained weight" is not a tremendous increase in me

That's true. However, by far the most common explanation for "I started eating less, counting calories, and I gained weight" is not a tremendous increase in metabolic efficiency, but a combination of: 1) spontaneous fidgeting and unscheduled exercise dropping off (sitting in your chair all day without getting your normal couple trips to the water cooler/bathroom, not shopping today because you're tired) - this is called "NEAT" if you want to Google 2) self-delusion as to the degree of reduced food intake The latter is the most likely cause of severely failing diets.