Hegel remarks somewhere that the great events and personages of history
happen twice, he forgot to add that they occur the first time as
tragedy, the second time as farce.* (See 18th Brumaire). But Marx forgot
to add that the third return is as po-mo.
All well and good, but "post-modernism" (like romanticism and modernism
before it) has become a catch-all term of limited use, and cavalier or
sweeping dismissals of it probably are foolish.
*Quoted from memory.