Where is the parent saying anything about meal timing? It's about the effect on your body of a particular meal. Carbs and sugars spike insulin much more than fats or protein.
That is an issue of meal timing. Individual meals doesn't matter. Transient insulin spikes are irrelevant, what matters is your overall expenditure vs intake.
Insulin spikes are completely relevant, since insulin signals your fat cells to take up energy from your blood stream. Now you have no energy and feel hungry again.
It doesn't work that way. Show me a study that concludes that blood glucose levels have not been meaningfully increased after a meal due to it all going straight to adipose tissue -- in humans -- and I'll show you the next Nobel Prize winner.
Insulin spikes are irrelevant in so far as you will lose weight at a calorie deficit, insulin spikes or not. Also, fat can be synthesized in the absence of insulin spikes. http://www.jlr.org/content/30/11/1727
Physiologically, what matters is a caloric deficit. Execution wise, some foods make this easier than others, but that is highly individual.
Steady levels of insulin make it much easier to maintain a caloric deficit. If your blood sugar is yo-yoing all over the place, you're going to get cravings, increase your risk of bingeing, etc.
While it's easy to fall back on 'calories in, calories out', weight loss has much more to do with psychology, physiology and compliance than physics.
You're absolutely right that losing weight has a lot to do with psychology, and that the execution of it depends on finding a method, a diet tailored to the individual's needs, to succeed.
But that diet will only result in weight loss if there is a caloric deficit, completely independent of insulin spikes. Now, the trick to achieving and maintaining that caloric deficit over a period of time is an effort that is psychologically demanding, absolutely. But the weight loss itself is pure thermodynamics.
If your interest lies in designing diets or meal plans that help people achieve their weight loss goals, your focus should rightly be the psychological aspect of it. That's the battle. But at the end of the day, a caloric deficit is necessary, whether you choose to ignore that or not.
IMHO, diet and nutrition is confusing as hell to the average person, and hiding the necessity of a caloric deficit and instead talking about "good" and "bad" foods or macronutrients, is a poor approach in the long run. But that's just my opinion. The necessity of a caloric deficit is not opinion though, it's cold hard scientifically proven fact.
> The necessity of a caloric deficit is not opinion though, it's cold hard scientifically proven fact.
It is not that simple. If you have a calorie deficit but aren't getting enough nutrients you will get cravings but won't be able to sustain your diet. If you're addicted to sugar you will get cravings/constant hunger and won't be able to sustain your diet.
Focusing on calories ignores all of the other things (nutrients, insulin, blood sugar, motivation) that need to happen for a diet to be successful.