But is the Western hero as much a myth as the noble savage of folk collectors?

I've thought some about this while trying to teach myself to write screenplays of my own.

I would say no neither is totally a myth. But with I have many qualifications, for that statement. There were some real western Heroes. On the other hand, there were also some noble "savages". Though savage is a very degrading and Eurocentric term. Wyatt Earp, certainly was a hero at times. Tecumseh was by the accounts I have read, a noble warrior and leader. In dramatizations of the most famous western story, the gunfight at the OK Corrall, it seems that the Earps are usually painted as better than they actually were and the Clantons get painted a little worse. The fact that it was a culmination of a political battle is often glossed over or ignored for the sake of the story.

There are archtypes used in movies that tend to exaggerate certain qualities in characters in order to make a more universal story or a more clear morality play. Hero, antihero, comedic side kick, damsel in distress are a few examples.

When dealing with historic material, the screenwriter often glosses over the parts of the bio that do not fit the archtype that the movie requires.