“He states that ...until the late 19th century, civilized soldiers were at a slight disadvantage in fire weaponry when facing primitive bowmen.I disagree.”
He’s wrong. Civilized soldiers were at a huge disadvantage when facing plains and southwestern Indians. It was not until the advent of the lever-action rifle that the tables turned.
Another advantage were the grain fed horses of the Cavalry. This gave the animals more energy and stamina than the grass fed equines of the Indian.