What you wrote here is spot on. While there was clear regional specialization, the country was very interdependent. Most of the wheat and corn that Southerners ate came from the Northern, Midwestern, and Western farmlands. As I found from one source, rich Southerners became land speculators in Yankee territories. Furthermore, a lot of money loaned by Northern banks came by way of England. Financiers in Great Britain were investing heavily in the growing economy of the United States.
I have dug deep (for a non full time historian anyway) and shown that contemporary sources, and more recent historical works, put the lie to the Neo-Confederate nonsense. Although probably primitive by today’s standards, economic activity was a lot more complicated in many cases than people tend to give credit for that era. I have read that shares of ownership of merchant vessels could be bought just as shares of company stock can be bought today. Southern investors were free to buy these chairs just as much as New Englanders could, unlikely did.
Of course no amount of factual information will dissuade those Neo-Confederates from their burning love of the Lost Cause. Some people just love a good conspiracy theory, in this case, even a weak one.
Here is my source for the breakdown of $200 million in Northern "exports" to the South, and here it is again in table format.
Curiously, except for smoked fish there are no food items on the list, and I'm not sure what that means.
I've supposed it means that most of the food items "imported" by, say, the Deep South came from Upper South & Border States.
This part you got right. Here's a simpler way to process the complexity. Look at inputs and outputs.
South put out 72% total value. New York takes in something like 90% of the total value.
Who runs Washington DC today? New York does.
Figure it out.