I know the game isnt supposed to be realistic.. but still a good logic can be applied for the armor -weapon system..
If i try to explain the armor system logically, this would be what i would use...
KEY:
Armor- bad, not so good, good
heavy - Pierce, blunt, slash
Medium- blunt, slash, pierce
Light- slash, pierce, Blunt
Explanation:
heavy should be (ideally worn by blunt weaponers)
bad against pierce.. because the heavier weight makes them slower against stab, thicker plates leaves more vulnerable spots to hit at, under arms and such... archers would be able to take them out before they get near them

not so good against blunt.. because blunt weapons would crack the heavy armor a lil and deal an average damage.. also they would know where to hit(blunt against blunt)
Good against slash.. because slash would just bounce off the plates
Medium should be (ideally worn by slash weaponers)
Bad against blunt..because the armor would "crack" like hell against them
Not so good against slash.. because slash weapons would "crack" the armor but not as much as blunt and deal an average damage.. also they would know where to hit(slash against slash)
Good against pierce.. because being less thicker it covers more vulnerable area leaving less spot to hit with pierce
Light should be (ideally worn by pierce/stabbing weaponers)
bad against slash.. because the sharp edges would just tear them off
Not so good against pierce.. because of sharp edges of arrows/bolts/daggers this will do an average damage.. also they would know where to hit(pierce against pierce)
Good against blunt... because the leather would act as padding and take the most of the effect of the hit away
Ideal weapon/armor combo:
Heavy Armor with Blunt weapon
Medium Armor with Slash weapon
Light Armor with Stab/Pierce weapon

There is not much change to be made.. only in medium and heavy i think.. please consider it.. instead of making people confused

i know some would say changing now would be more confusing.. but i think the positives are far more greater here in the long run..
If the prob is with the armor already being chosen now.. you can always given an option to players to change it ones more..

And a kind request to any DEVs who reply to this..
Please dont say bluntly that the fighting system wont be changed anymore :/ that kinda hurts whenever something is proposed *sighs*
A "We'll think on this" would be much better response"

i came to decision of proposing this after reading the confusion in this thread
