Good doctors tend to dumb things down. They're busy people, lots of patients to help, little time for trying to explain extremely complex subjects, particularly when the true explanation for something ends with 'nobody knows'. When they do write a book or appear in a YouTube video though they mostly talk about the subject of their own expertise, the thing they're qualified to talk about as an actual expert.
Bad doctors dumb things up. Plenty of time on their hands to try their hand at writing books on subjects they have little expertise in and appearing in YouTube videos talking about all manner of stuff. They often make up silly rubbish to fill in the blanks that re unknown or which they don't truly understand themselves, because they're not experts but have to appear to have good, interesting answers if they're going to sell their books. Just as bad, they often parrot silly rubbish they heard somewhere else, without either the inclination or the capacity (one or the other) to fact-check it. Offering novel medical advice on subjects they don't understand extremely well is pretty much what makes a bad doctor a bad doctor.
My very first post on this forum was on the subject of insulin resistance. Like you I wanted to understand it and was confused and annoyed by the lack of clear information available. I had some theories, which were very wrong. Like you I kept looking for information trying to understand more. We ended up choosing very different paths though, learning from different sources, and have arrived at different places.
From the first post in the thread I see you started with Dr Jason Fung's book on diabetes. Dr. Fung, the nephrologist, a trained expert in kidney diseases, who wrote a book about fasting diets for weight loss, and another about how his fasting approach applies to diabetes. Dr Fung, as I understand it, suggests in his book that a Type 2 diabetic can't easily lose weight unless they lower their levels of circulating insulin, because insulin prevents fat burning, so the solution is to fast and eat low-carb to lower insulin levels and enable the burning of fat.
Or something like that. I'm not sure what he actually says, because I didn't read his book, because after watching a couple of the kidney specialist's YouTube videos on the subject of weight loss and diabetes a quick bit of googling led me to the Rice Diet from 1939 - quick summary here:
Link It seems it's possible for a diabetic to lose weight and even improve their fasting blood glucose levels on a diet composed almost entirely of carbs! It seems calorie restriction worked just fine back then, but then I suppose they didn't have YouTube personalities to confidently inform the people losing the weight that is was impossible. I'm sure there's plenty of good stuff in that book of his - he is a doctor after all - but when it takes less than five minutes to find this hole in one of his novel medical theories I decided never to read it. It's sometimes hard to unlearn a falsehood; easier not to come to believe it in the first place.
Instead the path I chose was to read material written by experts in the subjects I'm trying to learn about. As a result of this approach I now understand that the Rice Diet lowers insulin resistance in the livers of Type 2 diabetics. It does this though weight loss, which depletes ectopic fat in liver cells, which makes those cells resistant to the effects of insulin. It is important to point out that insulin resistance means something different in the liver than in every other tissue in the body. Insulin switches off glucose output from the liver. When the liver is insulin resistant is doesn't reduce glucose output as quickly as it should, and this leads to a rise in fasting blood glucose levels. Deplete liver fat by any means, a high-carb, low calorie diet works just fine so long as the amount of fat exiting the liver in the form of triglycerides is higher than the amount entering it or being synthesised within it, and hepatic insulin resistance will fall. Insulin resistance in other tissues means something different, with the possibility of different causes involved depending on the type of cell you're talking about.
There is no good book on the subject of insulin resistance which is written by an actual expert. Well, there is, it's called 'Understanding Insulin and Insulin Resistance' by Professor Anil Gupta, but it costs £121 on Amazon and I haven't read it because that's silly money and it's likely so far above my head that learning from it would be extremely hard work. To the best of my knowledge Prof Gupta doesn't have a YouTube channel. There is however a cheaper way to get a handle on all we really need to know as Type 2 diabetics - here's some recent research on how Metformin reduces insulin resistance -
Link - something about Glucose Transporter 4. For simplicity, assume this applies mostly to muscle tissue as that is where most glucose uptake occurs (muscle tissue and the brain, though if an insulin-resistant brain is a real thing I haven't heard of it). The conclusion ends with the phrase "A better understanding of the mechanisms behind its clinically relevant increase in insulin sensitivity could help researchers and clinicians studying and treating the dramatic rise in IR conditions worldwide." In short, 'nobody knows'. Good doctors. I learned what I needed to know - Metformin lowers insulin resistance (not the liver kind, it has different effects in the liver) and nobody fully understands exactly how Metformin works, because nobody understands perfectly how insulin resistance occurs (and vice versa).
Unfortunately this provides a lot of wiggle room for bad doctor types to make up silly rubbish and sell books. Hence two of your three camps. Here's what I've learned and taken to be true as a Type 2: Losing weight and keeping the fat out of the liver lowers insulin resistance in that organ. Exercise lowers insulin resistance in muscle tissue. Losing weight and avoiding rapid weight gain may lower insulin resistance in adipose tissue (fat cells) and keep it low. Also, there is probably a genetic component to insulin resistance - most people who get a fatty liver do not develop impaired fasting blood glucose - in liver cells at least it's probably as simple as ectopic fat + genetics.
In short, eating less and moving more lowers insulin resistance. The rise in insulin resistance levels in the population could be as simple this: people are moving less and eating more than they used to. Car ownership and fast food outlets. Deliveroo. There might be much more to it than that for sure, but it's all speculation and BS right now because nobody understands insulin resistance well enough to understand how Metformin works. If understanding that is impossible right now at the current level of scientific understanding then identifying environmental or dietary causes of insulin resistance is impossible. There's little point wading through the BS looking for fragments of truth right now when you can just go for a nice long walk, which will lower your insulin resistance.