The Borg send one Cube out into the unknown like a seed knowing that one cube with a bit of luck can bring 'civilization" to large fraction of the acceptable/useful beings in the galaxy.
What we saw in the beginning of Scorpion was an exodus.
In one battle half way through the 2nd episode, 8472 had destroyed eight planets, three hundred twelve vessels disabled, four million, six hundred twenty-one Borg... And that probably only took a few 8472 moments.
8472 had been at this for over a year.
What we were seeing were not fleets per say but the remnants of planets and cities that broke off and feared complete destruction, as well as obviously defensive fleets, but really if a planet can be turned into a few million guns, why do they need ships?