High fat/high sugar foods offer the most calories/dollar. So what? If you are fat you have no reason to maximize the number of calories you consume.
Similarly, if you wanted to maximize your salt intake, you can get the most salt per dollar by buying a canister of salt.
It's much better than the popular notion of calories-in/calories-out, though.
Cals in/cals out has been validated in many controlled experiments to be a good first approximation. Taubes' insulin theories have been debunked by experiments.
Incidentally, the standard picture doesn't blame sedentarity as the sole cause of obesity. It blames the combination of sedentarity and increased caloric consumption as the cause.
But the cause, whatever it is, is highly unlikely to be some sort of metabolic disorder. Fat people have a higher metabolic rate than thin people, not a lower one. Their bodies release fat more easily into the bloodstream, contra Taubes and others. They just eat a lot more.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC303803/
http://onlinelibrary.wiley.com/doi/10.1111/j.0954-6820.1969....