I encountered a bug where all of the corpus crewships disappeared after destroying one with the forward artillery and couldn't complete the mission. This happened on pluto after doing one of the other side objectives.
Looks like the max gunnery level is still 9. Gunnery 10 ruined using the turrets for me and is a huge reason I don't play railjack missions anymore. Anything that takes control of the mouse is incredibly obnoxious and feels awful. I currently don't have any suggestions for making it better, but anything that affects aim should be avoided in my opinion. Improving accuracy or projectile speed (or range in the case of photor). As long as it doesn't take control of my mouse or aim, I'll be happy.