Rotating Children as Rigidbodies2D because transform rotation is too costly

Well it turns out to be quite the fiddling with the physics engine. But here is where I am stuck orjust need some timeout because I had enough...

2D Spaceship TwinStickShooter. I got like 300-500 pooled projectiles flying, homing and ricochetting at a stable fps of around 150 (hopefully it is my shitty laptop makes this drop to that low fps...).

I got a Problem with activating and disabling the Gameobjects, as this seems to be expensive.

Now I built a turret mounted on the ship.

The turret gets parented at a relative position of a child Transform. rotating this at some point becomes costly. I tried to replace the transform rotation with a rigidbody rotation, but whenI'm doing this, it doesn't stay put and I have to actualize its position, which is another pain, as rigidbody.position gets materialized in the fixedupdate cycle, so I can't just update it in the regular Update cycle.

I don't know If i'Il have to use a rigidbody without a collider, with a collider and what I have to do to make it stay put in position.

Am trying to align the rigidbody's velocity with the ship's, maybe that'll solve the problem, but I have just reverted to the transform solution. Am doing it tomorrow.

Right now I'm just stumped. Is there a better trnasform rotation solution I'm missing, because Physics2D.UpdateTransforms explodes when I push an enemy ship around, making it rotate... with just 5 ships floating around (each 2 turrets)

So, Any suggestions?^^

(maybe I could stabilize the ships rotation through the yet nonexistent AI maybe that will help to stop too much rotation. on the other hand: why is rotating so costly, that makes it such a big deal?)

Alright I leave it for you now, I got to get some sleep...