Earlier quoted context omitted.
How can something that can't be proven true be proven false? "Artistry" has no concrete definition and is entirely based on the opinion of the viewer.
It's easy. Blind test humans and ask them which one they find more "artful". Once the average person can not tell between an AI and human creators, the AI is complete.
And what happens when public perception of "artful" changes in 10 years - now the AI is not complete anymore?
You can't base a metric on something with no measurement.