Libramarian
Adventurer
It's important to differentiate between weight loss and fat loss, unless you're well into the obese range to start out then the gym will probably put on the pounds but they're good pounds. Along the same vein, losing muscle mass on a low calorie diet isn't doing your health any benefit.
I don't endorse dieting unless you're gigantic.
I think you're exaggerating a bit here. I think anyone at an "obese" BMI should be dieting with or without exercise, and anyone at an "overweight" BMI should be dieting + exercise.
There's some research showing that if you're overweight and muscular, you don't have the same risk of diabetes/metabolic syndrome as someone overweight and fat, but you still have an increased risk of heart disease compared to someone of normal BMI. Thin and lean is best for health.
I'm overweight by BMI despite looking slim and fit, so I understand how in the west our body standards are such that it's unintuitive how skinny humans should be for optimal health, but it is what it is. One shouldn't let the perfect be the enemy of the good of course.