Hence the title of this thread. Voyager weakened the Borg. There was a tranwarp conduit 1-light year from Earth, with multiple cubes on the other end. What exactly was stopping the Queen from sending those cubes through to assimilate Earth? That's right, writer incompetence.
It isn't writer incompetence.
As a writer and producer, why would you sabotage the future of the Trek universe and you're own job by assimilating Earth and ending any future of Trek?
No, writer incompetence put the transwarp conduit 1-light year from Earth in the first place. They put themselves in a situation that has no reasonable explanation as to why it wouldn't
lead to ending the future of Trek.