My interpretation was similar. The carb-sugar diet was never a highlight because it was a given. The article talks about primates that have high carb-sugar diets but doesn't explain why their brains remain so small compared to humans. Maybe they will eventually evolve? Maybe cooked meat / dense protein is the X factor? If so, that takes back to the beginning and highlights protein. It seems reasonable the combination of the two would be important. Protein enables muscle development, human evolution made us exceptionally well-suited for long-distance and endurance travel compared to all other living primates. This further improves are ability to forage and is just an evolutionary winning combination.

My curiosity leads me more towards, are their other primates that had similar / convergent evolution that independently discovered dense protein sources? Is homo sapien really just a path of singular linear "march of progress" evolution? Were there other marches of progress from other primates or any other species that we competed against or merged with? Those kind of questions become more interesting once you realize the diet combination that creates big brains

>about primates that have high carb-sugar diets but doesn't explain why their brains remain so small compared to humans. Maybe they will eventually evolve?

if they have abundant sources of carb-sugar, there would be no selection pressure to evolve in a particular direction.