I don't think it was an error at all to compare and see what could be done. It was the same general territory and geography, but increased now by nearly 5 times the size. Europe was a factor in the outcome in both, and with large numbers of loyalist fighting for the Crown it was in fact a Civil War. Washington was able to keep his army alive even after losing many battles and all the major cities in the Colonies (supply points) to the British. His ability to keep his army in the field allowed time to build allegencies with France, Holland and Spain; a major factor in the outcome of the war. The North didn't overwhelm the South with numbers, if that was the case they would have won the war in the first weeks. The area was even too large for the armies of the North to control and it fact they never controlled major areas of the South until the surrender (many areas of the Confederate South never saw large numbers of Union troops.)
Remember Forrest proved the Union army was the best supply source for a mobile force. He always seemed to have more at the end of an expedition than when he started.