This is the cookie-cutter flaw of confusing a part with the whole. It’s not applicable here, because the author doesn’t erroneously switch between a larger and a smaller group.

The author’s failure isn’t that he erroneously expands a correlation beyond what he established. It’s that he doesn’t establish a direct correlation between discernment and writing skill in the first place.

This can’t be the flaw, because the author’s argument never suggests that artists lack insight outside of politics.

This reverses what the argument is saying. The author claims that greatness leads to discerning criticism, not that discerning criticism requires greatness to be made. Also, the argument is about writers specifically, not great individuals generically.

The author assumes that, because people who are great at writing are discerning critics, the better you are at writing, the better you’ll be at criticism. But we only know that great writers have reached a threshold, not that there’s generally a direct correlation.