> But therein lies the problem: being overweight is so _unbelievably_ unhealthy that most problems would be resolved simply by losing the weight.

Failure to properly diagnose the actual problems makes it harder for the doctor to assist the patient in actually losing weight. "Lose weight" is an outcome, not a course of action, and choosing the most medically appropriate course of action to achieve that outcome is down to coincidence if you decide to skimp on proper diagnosis just because you think that the patient needs to lose weight.