I'd like to present You an idea about charged weapons. These would have "pre-load" mechanic, so warships could charge these right before battle, and then instantly fire at enemies. Preload does not mean, that it is "dat big, slow aiming gun". Aiming could be done swiftly (during preloading phase) on smaller devices, and then these instantly fire at nearby tiny ships, destroying these one by one at slow rate.
During battle, these would serve as solid, slow firing, devastating arms, capable of hitting any target.
While big guns are supposed to be slow, because these are "this big", preloaded weaponry are supposed to be slow, because of preloading phase. It does not limit the gun to be big to have low firerate, and thus deals better damage/aiming per shot.