Well the argument is that the F-School was a response to the German proletariat's unexpected and unwelcome nationalism in WW1, the failures of the post-war communist risings in Munich and Berlin, and the capture of the proles by fascism.
Disillusioned away from classical Marxism by above events, the F-School gave up on the proles as the identical subject/object of history, and they began to search for a surrogate revolutionary vanguard. They found it first in African-Americans, then in women, now in sexual minorities. So ideas like "cultural revolution" and "identity politics"--which no-one can deny are strongly influential on today's Western Left--originate with the F-School's revision of classical Marxism.