Exactly. The idea is to remain metabolically flexible. At the same time, a large part of modern population consume too much carbohydrates ignoring the fat thing altogether. Within 10 or 20 years of such diet, the glycolysis metabolic pathway often gets broken causing insulin resistance.

But it's not only sugar excess that makes that damage, primarily it's the lack of nutrients in processed foods that causes a gradual mitochondrial decline.

For instance, most people consume white sugar because it's cheaper. On the other hand, sugarcane consists of the same glucose + fructose combo as the white sugar but it also contains vitamins, giving us much better chances to remain healthy.

Fats still have some uber-abilities compared to the glucose though. The main one is the ability to "shortcut" the faulty metabolic pathways.

I will give an example. When glucose pathway is broken in a cell, it leads to inability to produce enough Acetyl-CoA in the given cell. Acetyl-CoA is an intermediate substance that is used by mitochondria to produce the ATP. When there is not enough Acetyl-CoA, the ATP output levels drop, causing detrimental effects on health and general well-being. Such cells start starving, degrade and eventually die.

When beta-oxidation pathway is broken, it leads to nearly the same defect, but this time for fats. However, if a person still has at least some number of cells that can do beta-oxidation correctly, those cells can "share" their Acetyl-CoA with other cells through the blood stream. This happens mainly in the liver thanks to the fact that the fats are so powerful that they cause a huge abundance of Acetyl-CoA. And that excess finds its way from the liver cells' mitochondria into the bloodstream, feeding other cells by "shortcutting" their broken glycolysis/beta-oxidation pathways.

The excess Acetyl-CoA from liver gets delivered to every single cell in the body, including the brain cells. Even if a specific cell has subpar beta-oxidation or glycolysis abilities, it still can consume the external Acetyl-CoA without any problem and produce the adequate amounts of energy from it to keep the cell healthy.

That's why a low-carb high-fat ketogenic diet has so tremendous effect on some health conditions - it allows to "shortcut" the subpar metabolic pathways in affected cells allowing them to survive and even heal over time. This is a natural cycle of the body and suppressing it with a sugar too often will cause serious problems over time.

Regarding high-carb low-fat diets: probably they can work given enough nutrients (minerals and vitamins) quite well, probably stretching those 10-20 years of adequate glucose metabolism well into 60-80 years. But still, you better be doing some fasting (or keto) to heal the accumulated damage, at least several times a year.

The obesity is a factor but it is not the cause. For example, Asian people may appear thinner than Westerners, but they are ridden by beriberi more often. (Beriberi is a metabolic condition that is caused by mitochondrial damage due to the lack of vitamins)

Regarding what blocks what it's a complex question. Glucose metabolism blocks lipid metabolism and vice versa for sure, but I have no specific data. From my own observations, glucose is much more potent in blocking the fatty metabolism than the other way around.