They give less PDF on a per slot base in addition to having to be replaced over time because vehicle scale gravshields* don't hold up when the other sides ship PDF start to fire.
*what it is, is defense against other strikecraft
They also cost way less per slot and can be distributed more widely and just offers more coverage in general.
Like we probably wouldn't want to spend 120 Psy-Scopes (60 guns per escort PD grid) just to get a Fatesever PD grid on a Ketch but spending 36-72 per capital scale hangar (3 squadrons) for a light cruiser whose strikecraft can can go support that Ketch or some other ship would be way more acceptable and gives all our ships the ability to get Fatesever coverage.
Meanwhile a Fatesever PD grid on a Combat Brig wouldn't be able to help that Ketch unless the Ketch either runs to the Brig or the Brig runs to the Ketch, both of which are surrendering your ships tactical independence.
The lower raw fire-rate matters a lot less too when the time where they'll be actively shooting will be much higher than a shipboard PD grid.
Given our intention is to design an interceptor armed with one or two of them we might not even give them anti-ship weapon so the likelihood of actually exposing them to ship grade PD fire isn't very high.
Barring us developing some truly nasty strikecraft ordinance our main striking arm will be our shipboard weapon batteries with strikecraft relegated to the nonetheless critical of handling enemy strikecraft and ordinance.
I'm not seeing a good reason why we can't do both? I can see the argument that we don't want to have to arm all of our future battleships with Fatesever PDBs, which is fine because we're likely to design a Galleon at some point in the future which we'll need to build from scratch.
But our current Brig's already use them, so refitting them won't cost anything, and as long as we're not putting them on things willy nilly I'd say we're fine for Fatescopes for now? We produce enough Fatescopes a turn for 60 fighters to get one each, our current stockpile is ~1800 and rising, and in a pinch a Forge action give us 300 more.
Fatetwister Cannons are a much better use of Psy-Scope weapons for our ships.
PD is already supposed to provide all-round coverage and while Fatesever PD would increase the volume of fire and lethality I think I've already made a pretty good case for why strikecraft can utilize them better.
Fatetwisters meanwhile aren't just incredibly lethal anti-ship weapons since they never miss and have a very high chance of dealing critical damage but basically remove any need for CIWB (system slot heavy) on a ship since they would be able to cover the entire ship unlike our other naval weapons.
Not needing CIWB means we have more System slots to work with and as such can increase the amount of PD grids we can fit onto a ship.
Also, as we saw with our raid on that Freeboota base this turn infantry scale Fatecaster weapons are really good in ground combat so we are likely to want to spend our Psy-Scopes on that too, it's not just going to be our ships and strikecraft that need them.
Speaking of strikecraft, the
only thing Fatesever PD's can do is kill strikecraft and ordinance really well.
A Fatesever Cannon equipped strikecraft however can not only do that too but can also operate planetside as a solid tank hunter and air superiority fighter since while Fatesevers won't do much to starships they can certainly wreck tanks and other ground vehicles.
But yeah, there are just so many better more versatile uses for Psy-Scopes and while I don't disagree that Fatesever PD would be extremely good at its job we have a limited budget of Psy-Scopes and I'd rather spend them on areas where they'd have the most and greatest impact.
