[Baron Munchausen]

Planets are terribly vulnerable because they are immobile. WPs need long range weapons, at least in games against humans. The AI is usually stupid enough to charge right in and take on a planet at close range. And yes, the PDC is absolutely vital to protect a planet. The surest way to destroy most planets is to just sit at the edge of missile range and fire away until the WPs are destroyed. If the planet has enough PDCs to counter the missile capacity of the attacking fleet then there is no option but to approach within direct-fire weapon and and risk losses. With mounts for WPs equivalent to mountsfor bases, that is very expensive.

I've also modded my AIs to use "High Energy Discharge Weapons" or the equivalent in special weapon platforms. These long-range weapons are even longer ranged with the WP mounts and absolutely devastating. Sometimes a ship can be gutted by a single hit.

The tractor/repulsor beams are an interesting weapon choice for a planetary defence. With ships, the size class of the ship determines what it can move. Does a WP get compared to the size of the ship it is trying to move or does the planet count as the firing 'vehicle' and any size ship can be moved? If the latter is the case then this has some real potential for defense. You could fling ships half-way across the map and break up the attacking fleet, or pull in one at a time from extreme range into close range where you could smash it.