I have managed to get through about half the essay so far in depth, (but without a printer it's not the easiest thing to read off a screen). From what I can tell, you've completely ignored Thomas Love Peacock's "Four Ages of Poetry".
Most people read Shelley's Defence as a "stand alone" essay, mainly because his editors decided to chop out the direct references to Peacock when Shelley died without completing the work. Unfortunately, most of what Shelley argues is a direct response to the Four Ages.
Still, it's fascinating to be re-absorbed into Shelley's thought processes, line by line. From your reading, it seems he is preempting a lot of 19th/20th C. philosophy along the way.