The Borg incursions were really just a ruse to tighten control of the population and to militarise Starfleet.
Think about it, the Borg only attacked with a single cube at a time, did some damage but were then miraculously halted by the courage and tenacity of the "military" just before the Borg won.
But these "attacks" scared the population enough that Starfleet was allowed to build Defiants, Promethus, Soverign class "star(war)ships"
THe first contact incident was mearly propaganda with starfleet rigging a holoship to simulate a Borg Cube then a Borg sphere, the time travel part was faked to show that even history was safe in Starfleets hands.
Think about it, we have seen the Borg throw dozens of ships to assimilate single Worlds or thousands to fight a war yet they send one at a time to assimilate Earth and why, Earth is not that important in the great scheme of things. Even the Federation is not.
Open your eyes people, the Federation military-industrial complex is the monster not these "cyborgs"