Look, as has been mentioned before, the point is big=survavibility. On a huge ship, I often have one or two of my best weapons, an engine, some life support, a sensor, and all defence. It doesn't matter if they swarm me with 20 fighters, not one fighter will survive, and I'll often take less than 5 damage. Because they just can't touch me.
If you're building big ships with an idea of putting on lots of weapons, then you're just wasting your money.