The game is far from historical correctness. We fight battles which are not medieval at all, we can conquer the world as Denmark or Scotland, we can send people flying in the air with a successful charge and so on. That is not a fault, otherwise the game could be a bit boring.

You said something about bows and guns which I found very interesting. I don't like it too but the game must rely on are rather simple mechanic I fear.
(Long)bows for example. Not very effective against plate in the real world (same for crossbows by the way). That was not so important in the old times as only a small percentage of medieval warriors wore plate. But in TW end game there are lots of troops clad in plate, a lot too much in a historical sense. So crossbows and bows must be made more effective than should be. Same for arquebuses: if they were made as effective in game as they were in the real world it would be fun killing. So guns are weaker in performance but fire quicker than correct. It's a game.

That said the use of gunpowder units on the British Isles was not far spread before 1560-80. Englands army f.e. was oldfashioned between c. 1500 and that date which changed rapidly with the war in the Netherlands and Ireland. Henry VIII ever had to hire foreign mercenaries with guns. So M2TW is not so far from history in the case of Scotland. Do the English in M2TW have arquebusiers? They too should not but ... it's a game.