A percentile split of about 50-60/20-25/20-25 (CHO, protein, fat respectively) in the realms of the slight caloric deficit required for weight loss combined with sensible exercise is generally effective for the goal of decreasing body fat.
The principal benefit of carbs is to acquire energy that's easily accessible in the form of glucose. When we eat foods containing carbohydrate, digestive enzymes rapidly break it down into simple sugars and ultimately glucose. The glucose is then absorbed and either distributed to cells and muscles with the help of insulin for immediate use, or retained as an energy reserve in the liver and muscles in the form of glycogen, or stored as body fat.
Although protein gives us glucose too, but that process takes much longer. Keep in mind that some cell tissues (eg. in the brain) depend upon glucose which is why one of the side-effects of low-carb diets is a reduction in brain function.
When your body needs energy it first looks for glucose from carbohydrates. If there is a solid amount carb glucose from food (ie. because you're following a low carb diet), the body helps itself to glucose stored as glycogen in fatty tissue. If more energy is needed, the body then burns protein tissue in the muscles. In short, the availability of carbohydrate energy prevents the body from breaking down muscle tissue for fuel.
Carbs are necessary, it's simply the type of carbs you choose. Stay with whole forms of carbs not processes carbs, those are the kind that get you into trouble because they're often loaded with unnecessary amounts of sugar.
If a ketogenic diet works for you, then by all means, stick to it. It's not necessary to lose weight, though.
It can lead to a bit lower function in some cognitive functions, but not by a whole lot. "Reduction in brain function" sounds a bit harsh to me.
Some people get a bit drained while on it, other's don't. For most it passes after a couple of weeks when the body has properly adjusted to ketosis.
The idea isn't that we get most of our energy from carbs so we must cut them out. The idea, at least now a days, is that you eat a lot of protein and get very full from that. So yes, this would probably work with a high protein diet with carbs, but I don't think there has been any research actually comparing no carb and carb with equal protein on weight loss.
that's a lot of carbs and very low fat. Why so many carbs? I get it if you're an endurance athlete with a lot of races, then you need a lot of carbs, but for most people, having higher protein would probably be better because it induces satiety and has a higher thermic effect of feeding.