Well, since you asked for feedback
Firstly, the devs said at this point no new ships would be added because it's too late in the development cycle.
Secondly, the way you have it set up would make this ship pretty unnecessary. LRMs more or less accomplish the same thing. Yeah missiles don't go through shields, but enough of them can drop shields very fast to make that part of it a minor issue. They have long range and can fire out of the engagement range of most capitals. They are weak and can be chewed up quickly by Cobalts/Kodiaks that get up close. They aren't quite expensive to mass produce, but you would need more of them to match the firepower of the ship you propose, so you would maintain the same relative balance.
Thirdly, the ship you propose is more of a hard counter than a soft one. At least, when I make the assumption that when you talk about it only being good against strong slow targets you mean some sort of accuracy system where it wouldn't really be able to hit anything fast. Because if that gauss gun would hit anything at long range, going through shields, and inflicting heavy damage on hull, well, it would be more of a supership. A good portion of ship survivability comes from the fact that as shields drop they mitigate more damage, while armor is a flat mitigation no matter what the hull hp is. So any weapon going through shields would drastically reduce the lifespan of any ship, even if the weapon itself did damage comparable to, say, a Kodiak. But anyway, if it would only be good against slow moving capitals, then it would be a hard counter because it would excel at taking out capitals and capitals only, while everything else would excel at taking it out
