I think you have to decide whether you want a game that is as authentic as possible or a game balance that ignores this. In the time in which 0AD is set, the navy was not as usable as it is today. After the Romans had practically the entire Mediterranean under control, ship development stagnated. Arrow ships did not exist in the traditional sense, at least you couldn't sink ships with them, at most you could set them on fire. In principle, all war galleys were designed for ramming or you tried to capture the enemy. Special weapons like the Corvus or Harpax could be added to the Roman navy. For example, I think it would be fun if you could add pirates to sea maps as an option, like treasures, which can get on your nerves during setup. And also, as with delenda est, I think a naval shipyard is better than just one harbor for all units. But that's just my opinion...