The historical films also represent the directors' vision, as they had to choose the lens/film/exposure/processing to interpret the image and get their message

The historical films also represent the directors' vision, as they had to choose the lens/film/exposure/processing to interpret the image and get their message across. 4K HDR would just gives them more knobs to tweak. A documentary has less control over what happens in front of the camera, but the whole workflow behind the camera is still completely under the directors' control.