What do you make of those which came after Augustus, that do seem veristic ? Like Nero, Tiberius to an extent.....perhaps not Claudius, but the Flavian Emperors certainly.
Your theory does fit with the sculptures of Julius Caesar after his death, mostly showing an equally virile, muscular, imperious man...with a full head of hair. Some of them even bear a striking resemblance to Octavian. (The one on the cover of my civil wars penguin classic for example)