However, Gopnik does need to be straightened out on some things.
"Ellington was a dance-band impresario who played no better than O.K.piano, got trapped for years playing "jungle music" in gangster nightclubs and at his height produced mostly tinny brief recordings." Well, 3 minutes was the recording time restriction, his recordings are no tinnier than any of the day and he played fine piano. As for his "jungle music," soon after the previous quote you say, as a positive trait, that he was "unafraid of seeming too 'African.'"
You also say that Ellington's "first hits now sound dated and chi-chi." Mmm. Perhaps if you were a bit more specific. I don't want to hear Satin Doll anymore myself, but I don't think that's what you're talking about.
More egregiously, you make a point that from the beginning, to find his sound, he often hired not "up to-date urban players, but often less sophisticated New Orleans musicians..." A paragraph later, you say that his 1940 band was pretty much the height of his achievement and cite soloists in that band including Ben Webster, Johnny Hodges, Harry Carney and Sam Nanton. Those "New Orleans" musicians came from Kansas City, Cambridge, Boston and New York City, respectively. What a buncha rubes. Guess when those johnnies-come-lately came on board? Webster: 1935, Hodges: 1928, Carney: 1927, Nanton: 1926.*
Otherwise, good job.
*[Later editorial addition: I think it's reasonable to think of Ellington's bands as big tent operations harboring different schools of stylists; surely one element contributing to the singularity of his music].