I think that is correct in terms of men, material, and logistics. The south and Lee never had a realistic chance of a conclusive military victory to back up the right of succession. It still would have been interesting to see what may have happened in terms of a settlement if Lee had prevailed at Gettysburg and had been able to flank Philly, Baltimore and/or Washington D.C. .
Although the South was falling way behind the North in technology. The Union was equipping units with repeating rifles like the Henry or breech loading single shot weapons. The South did not have the ability to produce the bullets even if they were able to get captured weapons.