I saw two significant design hurdles. The first is how to meaningfully distinguish guns as 'light' vs 'heavy' in the absence of armor-piercing traits. Just increasing the IMP/DAM numbers doesn't do the job, because there will always be some larger number of 'lighter' guns that will have the same expected damage output, and also be able to divide their fire more discretely. I decided that my 'heavy weapons' would have longer range and narrower fire arcs, making them more 'bad against small quick targets' than 'good against armored targets,' but kept relevant by the advantage of range.

The second hurdle was how to have a frigate provide defense against fighters without the Defensive trait or Aegis system. Such a ship can only reduce the threat of fighters by threatening them in return, and must be able to do so against the fighters' advantages of moving second and attacking first. It needed weapons of sufficient range that the fighters could not easily close and attack it without taking fire, or else have a reasonable expectation of surviving a fighter attack to return fire, or ideally both. Since it also needed to have enough firepower to accomplish something against a Destroyer, my design is more fragile than I would have liked, but I reckon it still has a 75% chance of surviving a fighter flight's attack run.

The rest was straightforward.