PD definitely needs shaking up. I went about it by removing PD cannons entirely, and forcing players to use small, normal weapons to try and shoot down missiles
Even with overwhelming numbers of defense ships, you have to get dangerously close to missile swarms in order to shoot them, and the missiles that end up just out of range are liable to move in and hit before you have a chance to shoot them.
Combined with leaky shields and armor, everybody gets damaged on both sides of the battle, and it works great!