If we agree upon this idea of the precedence of content in an art work then we recognize that one content is not equal with another content. Content is indeed relative. The ideas of the artist appear in his feelings and are thus expressed on the canvas. But his ideas are not necessarily the same with another artist's ideas, thus the relativity and when we speak about relativity we speak about judgment. Every individual judges but the judgments of different individuals generally do not coincide. So then whose judgment do we speak about in relation to the content of an art work? Or is there a way out to give all individuals a sort of viewing key that could lead them to judge less subjectively?
First we have to clarify what is being judged and also what are the parameters of the judgment. If history is a good reference then we see that the content of art works that resist the realm of time always makes sense out of the period in which those works were created. In other words, those works expressed the "Zeitgeist" in term of the knowledge of their period, they indicated how the worldview of their societies was shaped in that present and how it was starting to shape the future.
In animist societies, the content that is represented is what preoccupies all the individuals: food, sex, the sky and so on. In the times of the gods, the religious message is central and in initial modern times, the house and the landscape where one lives are giving its centrality to the idea of ownership and individualism.
So what do we find in later modern times and in our present day reality that is really shaping our societies?
Is there one central theme or could there be multiple themes?
I firmly believe that there is one central theme and it is "how does our universe function". Not only the universe far away, the macro view of the universe but also the micro view, the view of the infinitely small.
So the question of our times, at least this is my view, is how does our universe work from the infinitely small to the infinitely large and what is our personal place in all that. I believe that the central question that best characterizes our times for most of the individuals is "how do I fit in all that".