May I ask where you found this:
Weapon * (1 + Attk%) - Armor
As well as how you found the mechanics of armor penetration and figured out melee defense applies after armor? I mean defense reduction applying after armor seems correct but how did you get the formulas for the first two.
Here's a list of, mostly bugs, some things I found out (all on PC):
1) Abilities that increase armor do not work on front armor: It means what you think, they do nothing when you are being hit from the front and only work while being hit in the back. This makes most of these abilities/passives (Champion passive, Horn of Valor, Warcry+ and Trust the Steel included) currently useless. Horn of Valor also improves armor rating by 50% rather than 15% for 10 seconds, but still not the front rating.
2) Enemies do not get flanking bonus: Or at least most don't or I haven't found any. Perhaps specific ones do, but Bear mauls the Wolves doesn't seem to do anything. Nevermind, maybe do after-all but the RNG mislead me.
3)Guard is 25% of max hp: I think this is common knowledge but I read somewhere that it does not stack with +HP items. It does stack with the +200 HP belt for sure though at least.
4)25% Max Guard Vanguard Passive does not work: Instead it adds a bit to armor rating (but not front armor due to bug 1)
5)25% max Guard Champion Passive works, but bonus seems closer to 20% than 25%
6)Turn the Blade Works without shield: Just wanted to make sure, makes it pretty much the best warrior passive.