If you kill one Borg drone, another immediately takes over those tasks and the Collective hardly notices. Killing a thousand Borg drones can slow them down a bit as now they have to commit resources to assimilate replacements which, once completed, their work will continue as planned. The only way to defeat the Borg is to eliminate all of them, everywhere, all at once. A glorious pan-Galactic fireball of freedom. Happy New Year to our Human allies from the Klingon Empire.