I wasn’t trying to equate the northern and southern economies. Your points are well taken in the comparison of slave vs. non-slave economics. My point was rather that there were incidental factors that contributed to the lack of industrial progress of the south. In comparison to the north, the south languished economically long after the abolition of slavery. One of the factors was climate; it was just too hot and muggy.
Before and during World War 2, the south was a reservoir of labor for northern industrial plants. That reservoir migrated north, and was both blacks and whites. While you have the black migration recently celebrated in books such as “Warmth of Other Suns,” white migration was just as important. For example, Firestone built a war plant in one of our local communities. The labor force was largely obtained by shipping people here from one rural Virginia county along the Kentucky border. Those people gave the community much of its hillbilly character. There is a reason they built the factory here in Indiana instead of where the labor was.
Develop widespread air conditioning in the 1970s, and voila! You have economic and industrial activity in the south.
Back in the bad old days my Indiana relatives were very disparaging of those they called “Kentuckians” - white Southerners who moved North to work in the plants.
I was mainly addressing BroJoeK's statistics, which conflated agriculture and industry in a way that is less than useful. One compares agriculture with agriculture and industry with industry, regardless of whether the labor is free, slave, or a mix. (Also, I was using my phone, which makes it nearly impossible to say anything sensible.)
The diet, disease, and climate issues certainly affect productivity, independent of everything else. On the other hand, poor nutrition was to some extent a result of culture, reflecting both the emphasis on export-cotton production and the preponderance of corn as a staple food crop. It's possible to grow a fine, healthy diet in the South, as our present situation demonstrates.
I learned from my recent reading (Bio of Jefferson Davis, IIRC) that this was also true to some extent during the Civil War. Some poor whites, trying to cope with hard times made much worse by the war, figured that they could do better for their families by going north to find a job than by enlisting or being conscripted into the confederate army.