From what I see of the definitions pointed to here, I would propose to turn the synonyms around.
@Vitaly Mijiritsky commented that the classical definition of "copywriting" is mainly off-topic here.
@Patrick McElhaney said in his answer:
.. it seems all of our copywriting questions are about microcopy.
So maybe it should be that copywriting should be re-tagged to microcopy, and not the other way around?