According to Rossiana, David Ross, 11th of Balnagowan only had one son whose name was also David.
https://archive.org/details/rossianapapersdo01read/page/12/mode/2up
Several descendants of George Ross of Elizabethtown have participated in the Y-DNA testing & they are a match to one descendant of James Ross of Anson County and one descendant of Isaac Ross, Sr.. Also several other Scottish prisoners of war... George Brush/Bruce of Woburn & William Thompson, of Kittery. Most importantly, they are all a match to descendants of Chief of Clan Murdoch Buidhe Matheson.
That definitely calls into question this idea that George of Elizabethtown was descended from any Rosses of Balnagown.