-The borg will just bring more reinforcements from the other side of the galaxy - No they won't; they can't - not for the next 70-100 years or so - the subspace tunnels were destroyed, remember?
It wouldn't take them anywhere near that long. Voyager
's original 70-year estimate was from the very farthest edge of the Delta Quadrant, 75,000 light-years away from the Federation. Borg territory extends much closer to the Federation, as close as 30,000 light-years, and Star Charts
shows an offshoot section of Borg space even closer, a mere 5,000 or so light-years away (this might be the source of the Borg supercube from Resistance/Before Dishonor)
. And even the Borg's conventional warp drive is probably more powerful and efficient than Starfleet warp drive. So even without the subspace tunnels, they were probably within 15 or 20 years of invading the Federation.