As recently as 25 years ago an author's merit was measured by the quality of his writing and the content validity of his work. Good writing is not as subjective as one might think. I've always thought of good writing as lyrical writing. Lyrical writing has a beat to it. That means you can almost feel the "beat" as you read it.
Content validity was assessed like all measures of validity: Contruct validity, internal validity, external validity and predictive validity. Validity is made or broken by a failure in any one of these measures. Construct validity is when whatever it is you assert you are measuring, you are actually measuring. In forensic science, let's say I'm going to measure blood spatter, but my test to do that measures the size of the decedent's pupils. Well, that test would not have construct validity.
Internal validity is a measure of internal consistency. Let's say I assert that the number of knife wounds correlates with the emotion of the assailant. I then develop a theory where one knife wound to the stomach=rage. Well now, that's not internally consistent.
External validity is an assessment of how well my notions about any subject can be applied to other similar situations. Let's say I'm a veterinarian and my theory is that a fever in a feline is associated with an infection somewhere. When I test other cats and find a fever, I should find an infection somewhere, that is, if my theory has external validity.
Now we come to what many believe is the most important and powerful validity: Predictive Validity.. If a writer, scientist or theoretician comes up with a theory or states a premise, and that theory or premise actually preditcts the future, then the validity of that theory or premise is guaranteed valid.
At one time before the Marxist revolution overcame traditional America, any writer who published a book with demonstrated predictive validity, that book would take off like wild fire. It no longer does. A LOOK INSIDE THE PLAYBOOK's predictive validity is unquestioned by friend and foe alike. And of course it was expected to have all kinds of validity in that its content cost its developers $50 million dollars. Lots of things have changed since the Marxist revolution replaced traditional America. For one thing people no longer read, they watch their "screens." Screens spew out fluff like a baker's spigot. Attention spans are so short that Millenials can no longer attend to anything more than10 minutes at a time. And only then if their brain is on "entertain me" mode.