While I agree with your sentiment, ancient man was hardly a paragon of health and vitality, and emulating their diet may not be the best method to attain long-life and athletic fitness. Just because they were sugar-starved doesn't mean it's a good thing, or that 8 grams of sugar a day is desirable (Especially for an athlete). I mean, an apple alone is ~20 grams of sugar.
I also doubt they ate a lot of fresh produce in the winter, but does that mean we should all stop buying produce in December?
I don't think the diet of ancient man produced a lot of world-class athletes.