haven't read the book, so can't comment on whether or not Elijah Wald actually said this or not, but I don't think jazz really was "gentrified" in that way. The very existence of the work of Albert Ayler, Ornette Coleman, Eric Dolphy, late Coltrane, Sun Ra and free jazz in general just goes to show that if there was any gentrification, it only went so far. Most jazz musicians were well aware of European classical music. they didn't need anyone like Paul Whiteman or Gershwin or Gil Evans to guide them to it.