Purdie laments the heavy influence of the Northrup Frye school of theory on comedy, and the related theories of Frazer's Golden Bough and Samuel Barber's theory of Saturnalia, complaining that many critics accept the paradigm uncritically even though it is unproven. I will not argue with her assessment. I have not studied carefully enough the positions of the critics of Frazer and the Golden Bough to have a sense of whether her criticism is fully warranted.
By the same token, however, her own book accepts the paradigm of Lacan just as uncritically, and Lacan's theories are just as unfalsifiable as Northrup Frye's are. Alas.
My own criticism of Toole's Confederacy of Dunces does use the Saturnalian theory of carnival. However, I do not make claims that the theory is itself a valid way to interpret all carnival events. My claim is that Toole himself was aware of the saturnalian theory and wrote Confederacy with an eye to that theory. So the Saturnalian theme is in the book, whether or not it is a valid way to analyze all comedy. One can make that claim in the same way that one can analyze Eliot's "Waste Land" using Frazer's Golden Bough, without necessarily endorsing Frazer's theory. One can do this because Eliot was so explicit about being influenced by Frazer. Frazer's themes are in the poem, whether or not Frazer's theory validly explains all primitive agricultural rituals and all comedy based on those rituals.