I've created a small archipelago map with high water level and 6 Civs that have unique ships, because I wanted to focus on naval warfare. AI produced way too many land melee units, which were useless outside of boosting cities defense. That production could go to ships (which AI made a very small amount) or just buildings. AI combat was fine considering what it has, so the problem is mainly with production choices. There was almost no point in promoting melee ships to Boarding, so I just picked Dreadnought every time.