1) If you're firing at something 1000s of km away, a small recoil & a little bit of torque and you'll miss by some way if you don't correct your aim.
2) 15" shells weighed a ton (literally) - you wouldn't be able to put many in a destroyer without slowing her to a crawl, and if you tried it you'd make a very pretty firework display if the enemy hit your unarmoured magazines...
IMO the mount system is good. If you want to have starships built like Napoleonic ships of the line with numerous rows of small guns, go ahead, but I think I'll be 'borrowing' the idea of giving large mounts a to-hit penalty.
*re-engaging lurking device*