There is tons of studies showing our metabolisms all burn calories at extremely similar rates.

Study please? Here's a study that says almost the opposite of that. People's RMR varies among male/female, age, ethnicity, and current health status.

Other studies show that people's BMR might vary only 200 kcal or so a day. 1400 Calories a week is almost an entire day of food. 5600 Calories a month is almost 3 days of food. 67,000 Calories a year is almost a months worth of food. 200 kcal may seem like a small number but if your metabolism is on the slower end of the spectrum, not eating a whole months worth of food in comparison to a normal person is HUGE.

In addition, what works for 1 does work for all, its literal science.

Not really, food allergies and diseases like hyperthyroidism prevent some people from losing weight in this fashion. My mom has hyperthyroidism and losing weight is incredibly difficult for her, even though she restricts her calories and eats relatively well.

Burn more calories then you consume.

This is absolutely true, but there are so many ways to get there. Not everyone is going to eat fruit in the morning with yoghurt and quinoa. Especially if your lactose intolerant.

Spain is second in the world in terms of life expectancy and many people there eat bread with oil on it in the mornings, or a deep fried egg omelette with potatoes. Not to mention the amount of cured ham and cheese consumed along with wine and beer. Fried pork skin anyone? It's a popular tapa in many bars. You might see that and think "hmm that's not really healthy." But, generally as a society, Spaniards are way more active, walk most places and don't mind going up a few flight of stairs. So they burn those calories.

My point is, not everything is black and white.