> had almost none of the diseases we have that are all really metabolic dysfunction/diabetes at their root

True. Unless you were rich. Even heard of gout? But yeah probably somewhat accurate for the whole population. But again, not much to do with ketosis.

I mean is there any evidence even today that someone whose diet is primarily (~80%) grain and other plant products with a lot of carbohydrates can enter ketosis even when practicing "intermittent fasting" while consuming ~2000-3000 calories per day (e.g. the estimate for standard Roman soldier daily rations is 3,000-4,000)? Seems impossible...