I think it has more dramatic effect without showing the battle. We have the Enterprise crew talking with Admiral Hanson, and the comm line gets cut off. A While later the Enterprise arrives at WOLF 359 to find the debris field from the annihilated fleet, it's quite a shocker. Showing the battle and the carnage being caused, would detract from that moment quite a bit, especially for people seeing the episode(s) for the first time.
I guess though, they could revamp the Enterprise crossing Debris field scene itself. I guess they could also improve the look of the Borg drones.
Personally though, I'm not too fussed, it works reasonably well enough as it is imho.