Human takes at least 30min to make a half descent painting. AI takes about a hundreds of a second on consumer hardware. So right now we are already at a point where AI can be 100,000 times faster than a human. AI can basically produce content faster than we can consume it. And we have barely even started optimizing it.
It doesn't really matter if AI will run into a brick wall at some point, since that brick wall will be nowhere near human ability, it will be far past that and better/worse in ways that are quite unnatural to a human and impossible to predict. It's like a self-driving car zipping at 1000km/h through the city, you are not only no longer in control, you couldn't even control it if you tried.
That aside, the scariest part with AI isn't all the ways it can go wrong, but that nobody has figured out a plausible way on how it could go right in the long term. The world in 100 years, how is that going to look like with ubiquitous AI? I have yet to see as much as a single article or scifi story presenting that in a believable manner.