My two pence worth;
1) Mail is fairly good at stopping thrust unless you needle pointed weapons are used like rondel daggers. Even if the mail was penetrated it absorbed a lot of energy allowing the Gambeson to absorb the blow. Mail would not of been used for so long if it was not effective.
6) Basically I agree with the original poster except the mention of leather. Leather armour was never that common in western Europe. In general it [leather in genral] was more expensive (large scale farming of cows/bulls did not come until after the Renaissance) than fabric armour and protected less*. Whilst coir boli (boiled leather) armour did exist and was probable the earliest form of plate armour (before the transitional armours like coat of plates and brigandines) it does not seem to of been common or used for a very long period of time. Whilst Hollywood loves leather armour (mostly because it is cheap to make leather look armour using foam rubber) there is not much evidence for its actual use in western Europe during the Dark Ages or Medieval period.
*Despite a lot of speculation we do not currently know for sure the process our ancestors used to make coir boli and thus we can not be 100% sure how effective it was and organic materials degrade much quicker and more completely than metal armour so it may have been more common than we think but the lack of written sources would suggest it was not that common.
4) Also I am very suspicious about the claim that longbows could be shot like machine guns. Drawing a longbow takes incredible strength and its doubtful (at least to me) that a high rate of fire could be maintained for any length of time, also even the awesomely powerful longbow was not a long range weapon and after a few volleys the enemy would likely be on top of the bowmen and despite what we see in movies and games bows are not something you want to be firing in a melee. I would suggest that the devastating effect of longbows during the Hundred Years War was more a result of the sheer number of English troops using them than their individual effectiveness.
9) Early guns (known as hand guns) were I agree not a threat to knights (or really anyone else they were not that effective at all due to low quality powder and the lack of a proper gas seal resulting in much of the energy being wasted plus they were not aimed so much as pointed in the general direction of the enemy) they were not however cheap, black powder was very expensive for a long time and only the highest quality metals could be used to make guns (unless you wanted them to blow up in the users face). I rather suspect there main use was psychological rather than practical. As guns became more effective in both power and accuracy and cheaper armour had to get thicker to compensate the additional weight meant less could be worn. By the time we have personal firearms in common use (XIV century so not the time frame of Battle Brothers) they were quite capable of piercing all but thickest of plate armour. Eventually no armour was going to stop a musket ball and armour was simple to protect against melee weapons. By the XIX century whilst some troops did wear armour (for example French Cuirassiers) this was only for protection from melee weapons. No one put any faith in it stopping musket balls or even pistols at close range. The demise of the armoured knight was probable more economic than practical I agree but I feel the original poster is somewhat confusing the time line.
10) The Normans did not invent “castles”. Castle are simple large fortifications and fortifications have existed pretty much as soon as Human populations ceased being nomadic and remained in one place. The Celts build Hill Forts, the Romans build forts, the Ancient Greeks built forts. The Ancient Chinese build fortifications (Great Wall of China anyone).