I am not exactly a pro-carb diet expert, but I will play devil's advocate here (briefly 'cause I'm a little short of time today).
The Masai average 3-5 liters of milk per day. Depending on whether it's goat or cow milk, this is around 180-200g of CARBS per day. The Masai children are also rather fond of honey. Nuff said on that point.
Weston Price (one of my all time favorite observers) also noted that the people of the Hunza valley were the most 'superb physical specimens' of any he had ever seen (including the Masai). Their good health and longevity are legendary.......they eat MAINLY whole grains, dairy and fruit, with meat eaten once or twice a week when it's available.
Both the Masai and the Hunzas eat far fewer calories (on average) than your average western couch potato, and they have times of feast and times of near famine.
Both the Masai and the Hunzas, aside from dietary changes noted by Price, also invariably changed their other lifestyle habits as well (ie less active/more sedentary). It is impossible to disentangle the relative contributions of dietary changes and lifestyle changes to their declining health.
One last quick point, none of these people were 'bodybuilders' and even though they were relatively tall and lean, they were not overly muscular, but again they didn't weight train so who knows?
I think all you can conclude from analyzing the diets and health of different ethnic groups is that humans are an incredibly adaptable species and can thrive on almost any diet as long as it's rich in whole, natural foods and they don't overeat! This is a VERY hard challenge that even the Masai are now failing at when faced with cheap, easy and very yummy carbohydrate based foods readily available.
I 100% agree that endurance athletes can benefit from an increase in relative fat intake, but I for one do not wish to look like a world class marathon runner out of Africa who runs on the smell of an oily rag. The proof is in the pudding, and today's pro bodybuilders are building unbelievably muscular physiques using lots of drugs, carbs, proteins AND fats (almost certainly at cost to their long term health). Once again it just goes to show how adaptable we are! I follow the middle ground because my long term health is important to me, so I stick to low GI, whole food carbs where ever possible (including post workout and excluding cheat days).
Of course, the bottom line for fat loss is to eat fewer calories than you burn, and it hardly matters if you burn carbs, or fat, or both during exercise as long as your total fat burned for the day (including time at rest) is in deficit.