I'm neither a historian nor an economist, but all of your premises and conclusions seem sound to me (as well as morally strong).

I haven't read the article in question, but this phrase from one of the quotations makes me wonder:

"Unlike elsewhere in the New World, the South did not require constant infusions of immigrant slaves to keep its slave population intact." Perhaps Bourne discusses this elsewhere; if so, I'd like to see her support. The question for me is why didn't "forced breeding" serve to "replenish" the enslaved population in Central and South America? (Slavery of both indigenous people and Africans apparently existed in Canada but on a relatively small scale.)

Were enslaved Africans treated differently in Central and South America? What of enslaved indigenous people there?

For all I know, her spirit is in the right place, but like you I find her language troubling.