Well there is some precedent and reasoning for hull limits for large mounts. A 15" gun might fit on an ocean-going destroyer, but it's going to unbalance and perhaps capsize the whole ship when it rotates or fires, there won't be much room for the ammo, power for the turret traverse, etc. In other words, there are engineering difficulties, which would be different for spaceships but probably it is true that larger weapons would be more practical to mount on larger ships.
On the other hand, it also makes sense that some large mounts could be made for smaller ships. They might not be the same exact mount, however. For instance, a spinal mount on a destroyer is an interesting idea, although it would tend to be less accurate than a turreted weapon, because it would require the whole ship to rotate to aim it. However, a destroyer is more nimble than a battleship (at least in Proportions mod
), so that would tend to balance out.
PvK