well to go back to why not the gold fish with the forward guns (its a labored point but i think its important to the overall direction of weapon and ship design) , well because the ones used in skirmish mode are the common ships, in universe that is probably the first goldfish design, and they are probably old ships that have been traded, sold, or captured through the years. Updated and improved designs are are very expensive and the groups wealthy enough to have them would keep them close and only allow their very best crews to use them because to lose one would be devastating. Why doesnt every country in the world (irl) use the best weapons systems? cost. it all comes down to cost and politics. if you are going to argue for in universe logic, do not be naive.
In skirmish mode you are not the best of the best, despite what it may seem like, you are the average. if we were portraying the best of the best we would have the most advanced designs to work with.
the same principle holds true for weapon design, a new large piercing weapon would not be the hot new gun, it would have been the hot new design 10 years ago. these are the guns that have diffused throughout the world, they get the job done, they work, but they are not the best.
