well kraken idea was tossed in the mix as a instant death game mechanic that would make a player be wary going to the map borders and as a source of fear, becouse right now my biggest fear in battles is the wind and lack of ammo i dont particularly fear the ai ships killing me (though i still didnt make a playtrough in very hard and impossible mode )
as the boarding idea, you can make boarding harder by boosting crew of higher tier ai ships (my idea is that pirate crew is deadly against smaller warship, merchant crews but weaker than the crew of brig of war or bigger ships) plus limit the diversity of ships that we as a pirate player can buy so that the only way to obtain, lets say frigate, brig of war, brig, we can only obtain by boarding. this way as a smaller ship with a smaller crew we need to prepare a good crew and make good use of grapeshot ammo. you can expand this so the best ships we can only get when the nation that hates us sends a fleet to sink us. you can also limit the boarding mechanic by the the crew number if you have the minimum number of crew (crew that survived boarding) for both ships you can choose to keep it and if you dont have the numbers than try again.