What if ground turrets had to be built like a ship? They can rotate and shoot like a ship, but would have no ability to have shields to it. The way this would work would be similar to a ship, but the ship computer (the jukebox) would have a sign on it saying something like [MTurret], and they can be unlocked in the Defence Machines advancements tab. The turrets would ONLY be able to be built looking upwards, unlike how regular turrets can face down. Turrets would also be limited by block count, like how ships are. Instead of using carbyne (concrete), modular turrets would use stone bricks. This is just an idea, but I’d like to see something like it implemented.
I have twelve defense towers at my base, that work exactly or better then you just described. So what you are asking for already exists.