Of note I found the midlines somewhat easier to defend with a smaller fleet, assuming i'm actually present at the battle. My general strat for any station defense is to position my fleet on the left and right side of the station, preventing the enemy from surrounding it and giving the various modules time to drop flux before coming back around and blasting.
The midlines focus on overwhelming, if brief, firepower tended to mean that it'd just nuke a few ships each pass, thus making the battle easier, and then cooldown, while the other stations generally were a more sustained barrage.
That said the low techs insane PD tended to support larger fleets well which was kinda nice in the end game, but this is all just looking for flavor in what's otherwise a pretty meaningless distinction. They'll all murder anything but the strongest fleets, and do even more with fleet backup.