the question posed by robomatic
is partly addressed by
the scholarship of the late Derick Thomson,
in particular his 1952 work,
The Gaelic Sources of Macpherson's 'Ossian'.


Thomson concluded that while the stories of
Finn McCool, Oisin, Oscar and so on
were in fact centuries old
and thus not a figment of James Macpherson's imagination,
the literature that Macpherson published
was positively Macpherson's writing,
which had more to do with appealing to the audience of his own time
than in opening a window to the literature of another time and place.