While that is true there is variance it doesn't vary to the point of overcoming the basic thermodynamics at play. Facts are, you eat fewer calories, you lose weight. You burn more calories than previously without eating to make up the difference, you lose weight. There is no obese person that can starve themselves and not lose weight. It just doesn't work like that. The energy has to come from somewhere.
What often happens when people say "it doesn't work for me" is that they think they are working hard in the gym but aren't actually, or they think they are eating healthy without realizing all the little snacks or drinks they consume are putting some thumbs on the scale.
Sure the thermodynamic reduction of `weight-loss := energy-in < energy-burned` is true, but youre erroneously extending that reduction to assert basically ~variance in outcomes is explained by effort and measurement error~.
Most pointedly, theres a number of studies that measured outcomes from over/under-feeding identical twins [1] or varying exercise in identical twins [2] and found significantly wider variance WITHIN twin pairs than across the whole study. Phrased differently, calorie intake + exercise doesn't predict the outcome of weight even when controlling for hereditary factors, and looking at the geometric mean masks this.
TLDR the same amount of exercise + number of calories in one person doesnt predict the outcome in another. Hence why at-home delivery services doesnt eliminate the need for GLP-1 drugs.
[1]: n=12 twin pairs, Bouchard et al., NEJM 1990. [2]: "Mirror image experiment", Bouchard et al., Obesity Research 1994.