The intro to the article explicitly states that it will put aside any fanciful ideas that the technology might be better in the future; that "rather than try to forecast the future as it might turn out, I’d prefer to describe reality as it already exists".
The article acknowledges that AI progress to date has worked. It snidely disagrees without argument that AI the field could work from here on out.
saying it won’t improve isn’t saying that it won’t work. My car isn’t going to improve in the future, but my car will work in the future. They’re just two different things.