I would say Bark Armor is one of the worse types of armors. Its bulky and can easily break. Its best used for bludgeoning, but piercing and slashing can cause it eventually break. In fact that should be another issue. Weapon/Armor Breakage. Where their equipment can break and you must return to a city that makes the equipment to be come re-equipped.
hmm... armor breakage. I like it. That'd be one of those effects that would take a bit to implement but it can be done (and should be) and weapon breakages could be worked in as well.
My point on all that was to focus on the combat class allowed issue. You can certainly specify extra combat classes that can required for particular equipment types beyond just the Light category. You can also have a given combat class denied a particular armor they would normally by their general armor category be allowed. But I would suggest to try to design the system to be only as narrow as it must be and let the players decide what works best for them on their units. That will be half the fun, choosing between equally valid variations for differing strategic reasons.
I am not sure if rogues should be allowed to use any armors. Or if they did they get some sort of detection penalty.
Perhaps they could be set to no armor combat class but be allowed to select the Light Armor promotion which opens things up for them. But I do agree on that last assertion. That would be one of the more advanced effects to eventually be enabled but has been planned for some time.
I think it also depend upon what type of mount. Such as a horse archer should not have full plate armor. At the most they could have Lamellar Armor. And should we have mount armor too?
Oh absolutely, yes. But we would start with more a more basic approach by defining the differing types of mounted units as fast or slow. Elephants would be slow, horse archers fast, etc... this has other game bracketing effects but for armor it would certainly mean the slow mounted units would be more tending towards the heaviest armors, taking advantage of being able to protect their riders with heavier armor than one would want to walk any distance in, while the light ones would tend towards the lighter armors to keep up their speed.
Barding (mount armor) would certainly be a development but I'd want to have a mount equipment system in place first and your idea of equipment breakage would also apply there, so barding would mostly be providing resistance to attempts to slay the mount.
IRT Cord/Padded, I created examples just for the sake mostly of example. As you seem to understand the examples of iLinePriority assignment
methodology, I will then be quite happy defer to your effective research and game knowledge to generate specific decisions on how to categorize and grant access to the various armor forms, even which forms to include. I may negotiate a point or two but for the most part I can see a good partnership here in letting you create definitions on these things. I just need to make sure you're fully equipped with an understanding of the intent of the mechanism. Know what I mean?
To that end, here's a few tags we can consider in defining the effect values of a given piece of armor:
iArmorChange: Think of this as a percent modifier to the amount of damage the system would normally apply to a unit when that unit is struck in a round of battle. Thus this is basically a percentage value but can and should as it progresses exceed 100% and its opposing value, iPuncture, will grow somewhat in parallel in technological weapons development. Armor should also slightly exceed, on average, the equivalent contemporary levels of Puncture in the same age, variances making the system interesting. Thus an Axe with a very high puncture value of say, 25, negates the usefulness of say, a common Chain Shirt offering the unit 20 armor. But the arrows of the same era may have 10 puncture and thus the Chain Shirt reduces the Arrow's damages by 10% on each hit.
But lets consider some base values here for a moment.
5 - Thick skin like a bear perhaps, untreated leather, common padded armor
10 - Very thick skin such as that of an Elephant or Mammoth, Treated Leather, common leather armor
15 - Reinforced Leather, Common Studded Leather Armor
20 - Minimal bodily coverage but tough armor, such as a Common Chain Shirt
I'm sure you can work out further extrapolations from there.
iPrecisionChange: Precision is pretty much a percentage modifier to the chance to land a strike on the enemy every round in battle. For the most part, a point of accuracy is probably roughly equivalent in value to a point of armor or puncture. Armors would slightly diminish accuracy values based on how restrictive they are to the wearer who's making an attack with a weapon. Weapon choices themselves would modify this factor far more than armor would but armor would represent a non-existent to commonly minor to uncommonly fairly severe penalty to this value. Here, if we try to keep total modifiers within a range of -50 to +50 it would be beneficial to the system. Thus perhaps:
0 or no value here: Perfectly fitted Masterwork Leather, all silk armor levels
-1: Only very slightly impeding: Perfectly fitted Masterwork Padded
-2: Slightly impeding: Common Leather
-5: Somewhat impeding: Perfectly fitted Masterwork Chain Shirt
-10: almost annoying: Poorest quality Chain Shirt
This value is opposes Dodge values on the unit you're trying to attack. Thus Precision - opponent's dodge = modifier to your chance to hit.
iDodgeChange: Positive Dodge is not a quality of armor as all armor can do is impede, just as positive precision is not a quality of armor. But, like Precision (though the weapon can grant a positive if the weapon makes it easier to strike an opponent than harder, compared to punching the opponent, such as a sword may offer) those who wish to rely on their dodge abilities would prefer less restrictive armor and would, by unit type and/or by promotions enhance their dodge ability to potential heights.
Dodge impediments would be potentially more severe on armors than Precision, which is more a factor from weapons, but shouldn't really exceed much past -50 (which would be severe) in total on even the heaviest combination of armor, any penalties associated with the heaviest weaponry, and the heaviest shields.
Move changes: you're probably more in full understanding of the values of this mechanism than I am actually
And would thus know how to work with those values on armors to adjust movement in meaningful ways. Obviously Armor should only be able to provide a penalty as no armor would be the default.
iFatigue: Each point of fatigue is a % modifier that accumulates every round to the strength of the combatant. Thus even -1% over 10 rnds is a -10% combat modifier. Armors would obviously give cause for fatigue as they are simply more exhausting to fight in. Each point here is potentially very impacting, particularly if the opponent they fight is more heavily armored than their puncture amounts to (that extends the length of the combat # of rounds significantly) or if they don't have enough accuracy vs their opponent's dodge ability to land hits frequently enough to get the battle to completion fast enough before the fatigue really starts to impede them.
BTW, the opposite of fatigue is rage, like a berserker's fury, so some units by native and developed ability can counter these values and grow stronger as battle goes on.
So a truly unhindering armor would not have any Fatigue value perhaps, while the heaviest Light Armor, such as the Chain Shirt, would probably have a -2 or -3% value here. Modify this value with kid gloves and firm respect for each point!
Combat Class modifiers: You made a point about blunt, slashing, and piercing weaponry. The particular weapon a unit is using should add one of those three as a combat class to the unit. Thus the armor should have some combat modifiers against those using the combat class combat modifiers tag.
There's also Withdrawal modifiers and such for armors that greatly slow the wearer, particularly in a sprint.
Those are some thoughts for now as to the various ways to define differences in armors and an attempt to explain the meaning behind the numbers somewhat.
And that reminds me that Blunt, Piercing, and Slashing should be Combat Classes on our document list...