to be decided on Nostr: May be wrong here, but my assumption is: our ancestors, much like the relatives you ...

May be wrong here, but my assumption is: our ancestors, much like the relatives you mentioned (chimpanzee, ..) had a lifestyle that differs from the average modern human lifestyle in one key aspect. They probably had much more physical exercise (that was mostly inevitable) than people have now. (Another aspect is - I think - heating: people today mostly live in heated spaces which also reduces the amount of calories their body requires.)

I think this is an important (if not the most important) aspect that determines whether people can be healthy even though they're consuming lots of carbs/sugars, whether it be from grains or fruit or even sweet beverages.
If people easily expend all the energy contained in their food, due to their lifestyle, they'll mostly avoid the elephant-in-the-room health issue of our time: insulin resistence and diabetes.

With the typical modern lifestyle, I think, it's pretty easy to consume more calories than one actually needs.
Consuming more calories than one needs on a diet rich in protein-rich foods (meat, dairy, ..) is harder than on a high-carb diet.