So I’ll preface this comment by saying I’m a huge proponent of keto and it in no small part contributes to my profession as well as my lifestyle, but if the situation was honestly as cut and dry as your post makes out, then there would be no debate and every nutrition board would recommend a ketogenic lifestyle.
Yes, Ancel Keys’ research was flawed (some argue deliberately, others don’t), and yes, in some with type 2 diabetes, as the BBC documentary you reference suggested, keto can lead to a reversal in those symptoms (though to be accurate the documentary never referenced keto so much as low-carb). However, that does not mean that a) keto is the best dietary choice for everyone, or b) that it has no issues.
The best dietary choice for anyone is the one which they can stick to and that allows them to maintain a healthy weight (and gain muscle mass if they so choose). For some, this will be a diet with a high percentage of carbohydrates, and whole grains such as oats do have plenty of micronutrients which come with obvious health benefits.
Additionally, for a casual dieter, keto can be extremely difficult. Now admittedly, a lot of the reasons why could be mitigates via a nutritionally-complete ketogenic meal replacement (which would allow keto flu to at least be minimised if not eliminated entirely), but even with that aside, there are those for whom a fully ketogenic diet would not be appropriate. A brief example of this would be the small subset of the population who are sensitive to dietary cholesterol; whilst more recent research suggests the majority of people’s cholesterol levels are not really impacted by dietary cholesterol or saturated fat intake, a small subset do have such an effect. Due to the prevalence of saturated fats in a typical ketogenic diet (which for the majority are completely harmless, I hasten to add), this dietary type would not be suitable for them.
Getting 40% of energy from carbs is not the reason there are health issues now. The main dietary reasons for that are a) people are getting a large proportion of their calories from refined carbs and simple sugars which break down quickly, and b) our PUFA intake (specifically omega 6) and omega 3 to omega 6 ratio are awful nowadays, leading to many inflammatory diseases. Getting 40% of your energy from whole grains and fruit is unlikely to do any harm; getting it from chocolate eclairs and biscuits will do.
You are correct that carbs are the only one of the 3 macronutrients your body doesn’t need (well, to be more precise you don’t need the 4th macronutrient, alcohol, either, but it’s obvious what you meant), but that doesn’t mean they’re inherently harmful either. Some types absolutely are, but then so are some fats (trans fats).
Again, I massively advocate for keto, but it isn’t for everyone, and the evidence for LCHF vs HCLF certainly isn’t as clear cut as your post makes it out to be.