Why should we have assumed that their area of influence was confined to, and fully encompassing, the Delta Quadrant -- an area of space whose borders are defined by nothing but the result of dividing by four??
They've stated once the Borg are present in all four quads.
OK, scratch "confined to". Why does having a single point in an arbitrary division of space necessitate that a ship lost anywhere within that arbitrary division encounter them? If the galaxy were only divided into halves, and the conduit exited into the Beta Half, then anyone in that half must encounter the Borg? This is what Anwar is claiming -- that the writers had no choice
but to have Voyager go through Borg Central, just because it was the Delta Quadrant.