I'm not claiming it's rocket science, but there are always complicating factors. If behaviourism could be denied, obesity wouldn't be at the levels it's at.
There are other factors too - hormonal response and partitioning - some people, with surplus calories will be naturally predisposed to gain some muscle / LBM and little fat, whereas in others it can be a completely different outcome - and similar when in calorie deficit.
I know you are very intellegent, and feel I'm probably making a fool of myself but firstly what's LBM then:
I'm not sure what your saying, that hormonal factors effect your weight? is that just not as much as an excuse as "I'm big boned" seriously deprived people no matter their hormones are not fat, I starved to the point that I nearly lost my teeth, I could not swallow due to the ulcers, I was living on two slices of white bread, the cheapest, a day and the odd pancake made with cheap white flour and water as a treat, I was passing out many times as I walked through town and at college and kept making excuses. no amount of hormones would have helped, I was close to death before I asked for help
LBM - Lean Body Mass.
What I'm saying about variances in hormonal response, I'm talking about variances in how peoples' bodies react to food - how that can affect hormones that regulate appetite; how they react to excess, or deficit - is there any predisposition as to where excess may be partitioned (eg muscle, bodyfat), or where, preferentially, deficit may get used.