"It’s like Aeschylus, writing an episode of Undoners."

 Aeschylus was an ancient Greek playwright who is considered to be one of the great masters of tragedy. His famous plays include the Oresteia trilogy, The Persians, The Suppliants, and Seven Against Thebes. Presumably ‘Undoners’ is a soap or TV series set in the city Undone in the fictional world of this book. Perdita is comparing Daed writing a simple expansion to a great artist having to do something very mediocre and uninspiring.