What meaningful benchmark would you use? Art by it's nature is subjectively experienced - what one person considers great, meaningful, soul-moving art, another may consider terrible, meaningless, and empty. Both opinions are equally valid.

But if you're using AI to create art, you're typically not trying to move someone's soul. You're trying to create a work that depicts something in a particular style with a particular fidelity with a certain amount of resource consumption. That is the only metric by which it makes any sense to evaluate the machine designed to do that specific task.