Thinking about a man o' war solo campaign mode. Aside from the difficulty of making the ship ai work, it's also important to consider how mission failure and success feedback operates. I think the ability to take on missions of various difficulties from a pool would help (e.g. draw 3 mission/event cards, pick one.). The player can then be careful or greedy. The missions would have different threat levels, gold and score rewards.

As for missions, one can do a lot of interesting things that are a big no-no in competitive balanced play. There's no need to be symmetrical. They player can control their fleet while the mechanical opponent perhaps only has a few island forts, or sea monsters, or simply controls the elements and hazards like storms and maelstroms. A mission could have hidden or guarded treasures (like in Heroes of Might & Magic) and a time / "evil otto" limit. Lots of stuff becomes possible.