As a practicing musician so far I think he is right; music is a surprisingly difficult subject; in some areas (e.g. Bach chorales) there was astonishing progress in the last 20 years, in others none at all.
I think a group of multimodal agents could pull it off if they each were prompted to specialize in one instrument or facet of the music. They could iterate on eachother.
for a null hypothesis: Obama (born 1961) would have been 12 years old in 1973, for the release of both Pat Garrett & Billy the Kid (RIAA Gold) and Dylan (RIAA, ARIA, and BPI Gold)