Remember back in TNG when Borg Cubes dwarfed the massive Enterprise-D? Then in VOY they were significant;y reduced in size. Yeah what happened to them? With First Contact you have to remember the Borg had been battling the Federation ships for 3 and a half hours before the ENT-E showed. Data's admission that at max warp for the Enterprise from the Neutral Zone it would take 3 hours and 25 minutes to reach Earth. The Borg had been slaughtering the Fed ships left and right as we can see from the brief fight. Several ships blown up or being blown up, and DS9's great Defiant on fire and left powerless and adrift right when the Enterprise arrived.
If the battle was TNG Borg vs the Dominion you gotta give it to the Borg. Massive casualties for the opposing side with only one cube. If we use VOY Borg then we could see something like 2 dozen Borg cubes effortlessly blown up by the Dominion like Species 8472 did in VOY Scorpion. While Sisko praying to the Prophets to wish away an entire Dominon fleet left a bad taste in my mouth, I curse VOY for ruining the Borg.