Don't care what "Western Writers of America" or any other group of writers has to say about it. Writers aren't consumers of the product, and they have no idea what's good or bad.
Your opinion is that of a tiny minority. The WWA includes those who write screenplays for Western films; they know their trade. The script, cast, direction, cinematography, and editing are first rate. In addition to the #1 WWA rating, the AFI selected Shane as the #3 Western film of all time.