Gauguin paints, writes tracts, then frequents cafes and defends them. His audience, chiefly other painters, have a consensus about what is valuable and Gauguin moves the consensus.
Barney graduates college with a small corpus of sensational, techno-inflected body art that convinces a handful of consensus shapers (non-artists) of his importance. Every new work thereafter is lauded.
The canon follows cults of personality such as Barney's, each with its own market support system and curatorial coterie, operating disjointedly in a vacuum. Consensus is a series of habits of power, all being allowed to co-exist. (At least until the auctioneer's gavel decides ultimate value.)
In terms of a theory of post-history, the above is only taking place in McWorld. The Jihad continues painting pictures and photographing puppies as if nothing had happened.