I think some of you are missing the point here. Having the difficulty of a game increase as you get farther is a very basic, effective aspect of game play. It helps keep you interested in the game instead of frustrated. Don't use realism as an excuse, especially since it's perfectly possible while still maintaining realism, even if it's just making the player start in an area that has a higher concentration of weaker enemies. Having to scour the whole map looking for tiny bands of river pirates and running from sea raiders and war parties is not particularly fun or rewarding. Just a lot of clicking. If M&B was completely realistic, it would be an awful game where you'd spend most of the time getting dysentery.
Also, the excuse of "oh, if it's so easy just play solo and blind folded while trying to put out a forest fire" is annoying. That is not a solution. playing super mario galaxy with your feet does not make it a better game. A good game keeps challenging the player more and more.
M&B is an amazing game, but it could be a lot more accessible and a lot more challenging. Right now, when you get to the top, it quickly becomes repetitive. It makes you turn to mods very early. Now, mods are great, but M&B can be a whole lot more than just a "modding platform."