Re: Why didn't the Borg...
Yes the Borg could have quite easily destroyed the Federation if just one Borg cube kept most of the Federation finest ships at bay.
If we hadn't had the insight into the Borg world in VOY you could just explain it as being one of the mysteries of the Borg. Now it just doesn't make sense.
VOY ruined the Borg. They told us too much about them and one solitary little ship was able to best them multiple times. By the time the series ended the Borg were little more than a toothless old Grishnar cat.
Avatar: Captain Naya, U.S.S. Renown NCC-1415 [Star Trek: Four Years War]
Manip by: JM1776 (STPMA.net)