It wasn't THAT long ago, or THAT far away...
I believe she did mean to evoke the image of a (mostly) benevolent aristocracy overseeing a culture that she -- and many others -- saw as not utterly demeaning in every aspect. That is, she and her surrogate Scarlett, realized the culture was caught in a supply and demand circumstance, no matter how uncomfortable it might be.
Those who truly study Southern history, both Antebellum and Reconstruction, know that freedom was eventually the only humane course to pursue. But the cold turkey method foisted on owners and slaves with no transition to independence for either, was brutal for both.
I believe Mitchell wanted that story told and she succeeded brilliantly, through enduring characters against the backdrop of a bloody four-year war that found no real winners.