Most people on here are probably spending 10hrs/day in front of a screen, though. And in that case, more calories is unlikely to be the answer to a lack of energy/focus.

Endurance athletes are getting frequent and strenuous exercise. Most people don't. There's a lot of concern and advice in this thread about diet, but exercising more is the step that's missing. We live in the hydrocarbon era of easy transport, which means cheap food and little exercise. Both of those have to be addressed for good health, not just the food.

The analogy between salt and sugar does not really work.

Sugar is not an essential nutrient. You can eat absolutely no sugar without any ill effect. If you eat some starchy vegetables, that provides all the carbohydrates you need.

Even if you want to eat 6000 kcal as carbohydrates, you can eat that easily from rice/maize/bread/potatoes etc., with no sugar. In fact it is much easier to eat a huge amount of food when it does not contain sugar, because even if sugar is addictive and makes you crave for it, when you eat too much sugar during a short time, it becomes disgusting when you try to eat more.

On the other hand, if you stop eating salt, or even if you just eat too little salt, you will die soon, and not in a pleasant way (e.g. one of the symptoms of hyponatremia caused by eating too little salt is severe constipation, because various muscles, including the muscles that are used for the peristalsis of the intestines, lose their strength).

Like for any essential nutrient, both eating too little salt and eating to much salt is bad. The recommended daily intake of salt is between 4 and 5 grams of salt.

In order to be able to control precisely the daily intake of salt, I prefer to not add any salt to food during cooking (and I do not buy industrially made food). Instead of that, I add the salt only immediately prior to eating, so I can know exactly the amount added during a day.

For cycling, sugar (really a mix of glucose and fructose, which sucrose or sugar is an even mix of) is a necessary component to a fueling strategy because even a marginally fit individual will burn more in an hour than can be processed by the glucose pathway alone. The goal isn’t to meet some daily allotment, but to get as much high GI carbs into the bloodstream as your gut can take, as fast as possible. This has been linked to higher performance and reduced fatigue in the literature, not to mention this is what 100% of pros do (there are no keto pros).

One benefit of this, like you say, is you develop a general disgust for sweets and have no interest in them outside of training.

You are right, but this is a very specific circumstance when the required power output is so high that it exceeds the capacity of the intestine for glucose absorption.

As you say, in order to achieve the maximum power output that can be sustained for a long time, i.e. in aerobic effort, you also need fructose, i.e. sugar, besides glucose, to reach the maximum rate of carbohydrate absorption in the intestine.

However the vast majority of the humans may never encounter during their entire lives a circumstance when they need to produce a sustained power output so high that it is limited by the intestinal absorption (and without an appropriate training their muscles would not be able to sustain so much power anyway), so they never need to eat sugar. They eat it only because it tastes good.