I don't think it's that bad.

There is definitely an arguement to be made for the existance of the Jomsvikings. Considering that they're likely to be an elite, fairly uncommon unit, giving them extravagant equipment (like a horned helmet) doesn't seem that unreasonable.

As for the Sherwood Foresters, that's also within reason. While historical records are, at best, extremely limited, there are claims that Robin Hood existed in some form or another. Even if he didn't exist, guerilla warfare was in practise, albeit in a limited manner. I think that works, especially seeing how you can't directly build the foresters but can only recruit them through rebellion and bribery.