Yo, you are spotting off too much keto/low carb nonsense that you read from Charlatans. It's totally correct that processed sugars are a huge risk factor for a variety of diseases, no debate on that.
You can't use pre WW2 times for a few reasons. One, people back then were substantially slimmer, often even underfed in many cases. They also often worked physically active jobs and the food they ate would have been various types of grains and cereals, seasonal fruits, vegetables, potatoes, meats, dairy, etc. They ate a diet that was heavy in starches/carbohydrates that also included animal foods but they weren't eating large amounts of fat. People back then also had a much lower life expectancy than they do today, reasons for this would be the lack of pharmaceuticals, infectious diseases, etc. You also can't say they did not have heart disease because the data would not have been as readily available as it is today. People in this time period definitely had heart disease, strokes, etc. but they also weren't guaranteed to be living until 70+, it was quite common for men to die in their late 50s or 60s.
The eskimos were incredibly unhealthy. Those living the traditional lifestyle had a life expectancy of 27 and frozen "mummies" of them had undergone autopsies and they found atherosclerotic plaque. They had a deity in their religion that was a "fart god" who would bless you by giving you bowel movements and curse you by giving you constipation, this is due to their extremely low fiber diet. When they started eating a western diet they would have left their traditional lifestyle and lived more like you have now. This means they are going to live longer, so of course having heart disease and diabetes, which natives are prone to, will erupt.
You also have to factor in genetics, it's pretty well understood that non Europeans do NOT handle a western style diet all that well. Some really good examples are African Americans having much higher rates of hypertension for instance. Another example is how pacific islanders, like Samoans and Hawaiians, have incredible rates of obesity. Granted, there are other factors at play related to poverty but genetics are a huge part of this.