Mark Pimentel's lab which studies disorders of the gut has hypothesized that people with extremely slow transit times can absorb 2-3x the amount of energy from food in comparison to people with regular transit times. I think there is a high amount of variability; and importantly in the context of losing weight, people who are overweight often have slow intestinal transit due to their dysregulated gut microflora.

I'm sort of with you, but it sounds more to me like: start eating less, and you'll lose weight; eat more, and you'll gain weight. There's just too many variables here that change how food is metabolized and digested; including the microbiome which CICO ignores.