[Suicide Junkie]

Ok Point-defense cannon sounds like a kinetic-kill weapon. So, how about splitting PD into a short range, high damage, kinetic weapon; and a long range, lower damage, energy(beam) weapon.

Ie.
PD Cannons: 50% more damage than now, but limited to range 2, with maybe 3 range at max tech

PD Lasers: half-damage, but extending to range 8.

So, Cannons will defend the ship they're on, while the lasers defend the whole fleet, but less efficiently.

You now have more variety in defensive devices, and have to decide which will be better in each situation.