In general, I don't have a problem with your opinion for all human endeavors. I readily accept that many of them can be optimized and automated, indeed freeing humankind to pursue worthier goals.

I'm specifically objecting to your notion of art.

The advertisement industry is not a good analogy. It can indeed be improved, possibly by automated means. In contrast, the progression from "good" to "better" art doesn't work like that -- if it even exists at all! What is your measure of quality, anyway? Complexity? But sometimes minimalism is preferred in art. Maybe how many people like it? It doesn't work either; a lot of people like stuff that is not enjoyed by the majority.

When is art "better"? How can it be "improved"?

PS: the Sci-Fi market is already flooded by below-average human writers, so we don't need an AI to picture this nightmare scenario of good SF writers struggling to sell their books :P