The true answer is that the dialogue is all of these things, because it is none of them.

It is neither more nor less than the living picture and account of an original, drawn by a man of genius who was accustomed to observe human nature and society with a free unblinking vision, and to meditate upon them deeply and searchingly.
Diderot goes to work with Rameau in some sort and to a certain extent as Shakespeare went to work with Falstaff.

He is the artist, reproducing with the variety and perfection of art a whimsical figure that struck his fancy and stirred the creative impulse.

Ethics, aesthetics, manners, satire, are all indeed to be found in the dialogue, but they are only there as incident to the central figure of the sketch, the prodigy of parasites.

Diderot had no special fondness for these originals.