Update1.5.8 the A.I does NOT use the land paths to get to your base they ONLY take the nearest port to them to get there. This can cost the bot the game and is boring because they spend a lot of there turns sailing back and forth to your land from the far away ports even if the only thing between u and them is a simple road gate and u are basically touching . THE AI NEEDS TO BE AWARE OF THESE GATES AND PORTALS MORE. while they are sailing around i found it vary easy to take the hometowns of these bots on every difficulty quickly ending the games i was playing iv also noticed the AI has almost no understanding of defence and just buys every upgrade avalable to them in there town in order they appear in the menu xD they need to be a lot more aware of the simplest ways to reach u and your land such as going trough a land gate by force or using a portal i have had games where weeks go buy and the bot on challenging just sits in his lands doing almost nothing but still spawns huge army's out of nowhere with almost no income or resources please make them better alow them to conqure the lands around them better and make them less of a pirate norscan AI who love the ocean only and fear the land and its landlubber contents because really these pirate AI blow hard and are of no challenge i want an AI thats gonna come knocking down everyhting i just captured and connect his land to mine in an effort to bleed me dry of income not a bot that spawns 5 armys from nothing after a few weeks go by because he was porgramed to lol
I've also been thinking about the boat problem and my temporary fix was to generate custom maps without ports. It is not perfect and wont solve the other problems you mentioned, but at least the AI wont spend the entire game boating. In my limited experience, the AI also sorted itself out a bit, the game's pacing felt a bit more natural and I even had an AI eliminate another AI.