not so much an issue with full plate armor but with other types of armor especially ones that didnt cover everything, there was indeed a way to "wear" the armor. soldiers were trained to slash at an enemies exposed inner thighs, that meant pretty much instant death. in turn soldiers had to keep from exposing such weak areas to the enemy. that is essentially using your amor skill. while it doesnt take as much practice as learning to shoot a long bow. if you have to warriors who equally trained but neither has ever worn heavy armor......put a suit on one of them and i pretty much guarentee the other guy is simply going to wait for the turtle to wear himself down and then hit a weak spot such as the visor or underarms. there was also a portion of a medievel training manual which was thought to be a training guide that showed getting knocked over and getting up quickly while wearing a bunch of steel.
They got up quickly because the armor wasn't that heavy or restrictive. Hell, knights could do backflips and jump onto their horses in full combat armor. It weighted less than a modern soldier's kit, and it was strapped all over a person's body.
On the other hand, it adds a little color to the setting to help differentiate between the tame, civilized urban areas, and the areas effectively outside of the reach of imperial law, where every other person straps a blade to his back for protection. And it's a reminder of the drawbacks of the Empire -- how much of an obstacle it can be if you're on the wrong side of law or, (more likely, as an adventurer) the wrong side of the elites' idea of "order".
As for poorly armed civilian defeating armed U.S. forces, I believe you must not be well informed about Vietnam. We were defeated by a bunch of poorly armed civilians, not because we were outnumbered, not because we were out gunned. We lost Vietnam because we thought they couldn't win, and we got out thought. The tactics the Viet Cong used were far more thought out than we imagined, and they made American Morale deplete. In any war either side can win, if they play smart, regardless of resources, so I would not underplay the position of a government to step in. Especially in a more middle ages like environment, where the same spectrum of weapon capacities don't exist. Its much easier to fight a man who has a sword, shield, and full-plate with a knife than it is to take a tank with a pistol. So the threat is ever more real.
Plus magic can't really be regulated easily so I'd imagine that that downplays the empire need to regulate arms and armor because anybody who wants to learn to fight, but can't afford a weapon, might not have a hard time learning to use some simple spells. The fact that most prisoners come out of imperial jails knowing to cast a fireball spell speaks to the fact of how easy it is to learn some simple spells.
As for Vietnam, you are correct. They succeeded because they were willing to do things we weren't. Of course there is no doubt that the U.S. could have prevailed in the Vietnam conflict, but the result would have been several times worse for the populace.
Yes, but those games were developed with such content in mind. Your talking about stuff that goes into the development of the tools that go to be used in the development of the game. You have to modify the toolset to effectively implement it. It'd be like building a house and then deciding when it was finished that you wanted a basemant. A basemant isn't some advanced piece of technology, but you might have wanted to decide that you needed one before the rest of the house was made, because changing that after the fact is a lot harder than developing with it in mind.
Attack strength should be based on momentum and the type of weapon. Some weapons are not able to penetrate some armors, they will bounce off of them, but they still carry over the momentum, this is why blunt weapons would be effective in some situations a sword isn't.
Armors could simply be based on a calculation, take the armor material (this in itself having a few variables like flexibility, mass and special properties) + it's thickness + the quality = maximum resistance/weight. The craft type can determine against which attacks it protects better, some are better against stabs, some better against slashes, some better against blunt impacts, also how "cumbersome" the armor is (some armors being harder to move in, having more mobile parts or stiff plating). Plus some material have different capabilities like leather being fireproof but also protection against heat better while metals transfer heat.
Of course locational damage should come into this too, a glove doesn't protect your head, wearing a chest plate doesn't protect your back. Only wearing strategic armoring can be a huge advantage as it gives you more mobility and weighs less.
Like this it wouldn't even need a full out physics based system, the armor is simply based on values it adds up to numbers, and for the damage it does the same process (speed of attack, weight of the weapon, center of weight, sharpness...). The only physics it kinda should take into account is where you hit and the relation between you and the target (targets movement, angle of the hit...).