Carbs are not essential indeed. But consuming carbs when available gave us net selective advantage, which is why it's been the biggest part of our post-agricultural diet. And those carbs didn't exist in isolation but in the context of other macro and micronutrients including vitamins.

Can't say the same about caffeine sources, they weren't consumed for their nutritional content, and the supposed selective advantage of their consumption apparently didn't matter as much as carbs'. We didn't witness a supremacy of caffeine using populations, but we witnessed ones that could utilize carbs.