I have a few inchoate ideas, but rather than attempting any sort of peremptory answer I’m going to put your query to the other readers of Anamnēsis. Perhaps an interesting observation or two will emerge, and then we can all compare notes. To be sure, it’s a provocative question you raise.
You wish to know whether—and if so how—A. K. Coomaraswamy escapes the charge of self-contradiction. On the one hand he writes that “Dante’s theory of art … is … essentially Scholastic”, but on the other hand he also says that “from the Scholastic and Indian point of view, any … reflection of the person of the artist in his work must be regarded as a defect” (The Transformation of Nature in Art [Dover, 1956], pp. 177, 178).
Dante’s person, even personality, seems central to his great Commedia. Are we to conclude that his poem is to that extent defective?