Alright, I spent some time looking up how damage model works in Harnmaster. I am not previously familiar with the system and don't have any rulebooks, I just read someone's hopefully accurate player's handbook style rundown of it (here:
https://batintheattic.blogspot.com/2020/04/a-walk-through-harnmaster-combat-part-2.html). Previously only technical description related to URW's damage model I had read was the short bit on URW wiki which claims weapons get 1d2 damage dice per their damage value, but I knew this to be wrong from experience since weapons can regularly penetrate more then 2x their damage value of armor.
It seems what actually happens is that the relative results of the attacker's and defender's rolls are compared and then you get to roll 1-3d6 + weapon damage value vs. armor (with extra d6 if the defender counterstrikes or ignores). I'm not sure how directly this is translated into URW but it matches my experience of actually playing the game quite well. As I wrote before I think 10-12 represents well protected but by no means immune while 18 starts getting to the point a part is immunized. A Njerp with a scimitar with 5 edge would indeed struggle against 10-12 protection, though he could get through even 12 if he gets above average roll on 2d6. And a 3d6 roll with decent result would be required to get past 18.
That aside, why I'm really posting again here is that I put together some figures for comparing armors as systems with the various modifications I suggested here. I assume that both mail and iron currently get +1 to both point and edge protection at masterwork, just like leather does. I also assume that there is no hidden buff or anything similar specific to metal armor, in my experience a point of protection is a point of protection no matter where it comes from, but I admit I have not tested that and it's just an impression formed over course of normal gameplay. All furs will be regular quality bear furs, all other items are assumed to be masterworks, so this is intended to demonstrate maximum achievable protection with these sets.
The first set is the one I previously described and will be referred to as "battlewear". It consists of: Leather cap, fur hood, spectacle helm, long mail cowl, cloth cowl, fur shirt, leather shirt, leather cuirass, fur overcoat, fur mittens, mail mittens, leather forearm guards, coudes, leather belt, fur leggings, leather leggings, kneecops, leather shin guards, leather boots, woolen socks, woolen footrags and linen footrags. It weights 72 pounds.
The second set is what I call "mail set". It consists of: Leather cap, fur hood, spectacle helm, long mail cowl, cloth cowl, fur shirt, mail habergeon, coudes, leather forearm guards, fur mittens, mail mittens, leather belt, fur leggings, mail leggings, leather boots, woolen socks, woolen footrags and linen footrags. It weights 81,7 pounds, significantly more than the battlewear. It also has significant cost: masterwork mail habergeon and leggings alone cost 1000 squirrel furs. I don't think I need to count the price of every garment in the battlewear set to tell this is much more expensive. It is intended to represent a realistic heavy armor set, the kind which warrior would wear if he could buy it.
This is the protection that the battlewear currently has:Skull: 22 point, 27 edge
Face: 12 point, 14 edge
Neck: 10 point, 14 edge
Shoulders: 16 point, 19 edge
Upper arms: 10 point, 10 edge
Elbows: 15 point, 17 edge
Arms: 13 point, 13 edge
Hands: 9 point, 12 edge
Chest: 14 point, 14 edge
Waist: 14 point, 14 edge
Hips: 21 point, 21 edge
Groin: 21 point, 21 edge
Thighs: 10 point, 10 edge
Knees: 19 point, 21 edge
Shins: 15 point, 15 edge
Feet: 7 point, 10 edge
Pretty decent right? If you are feeling silly (more silly than to use three pairs of socks as foot armor) I suppose you could throw couple of tunics or undershirts there as the upper arms and thighs are the weakest spots to which something can be done. This would give those areas 12 point and 14 edge protection. It would still be lighter than the mail set.
This is what the mail set currently has:Skull: 22 point, 27 edge
Face: 12 point, 14 edge
Neck: 10 point, 14 edge
Shoulders: 15 point, 21 edge
Upper arms: 9 point, 12 edge
Elbows: 12 point, 14 edge
Arms: 10 point, 10 edge
Hands: 9 point, 12 edge
Chest: 9 point, 12 edge
Waist: 9 point, 12 edge
Hips: 22 point, 28 edge
Groin: 22 point, 28 edge
Thighs: 9 point, 12 edge
Knees: 9 point, 12 edge
Shins: 13 point, 16 edge
Feet: 7 point, 10 edge
The extra protection on the hip from the combination habergeon and leggings is more than a bit wasted since it was already so high. The shoulder is very iffy too. The upper arms and thighs are better protected, but the battlewear has enough free weight to more than make up for it. The torso protection is weak compared to the battlewear. This set is a downgrade: you pay and wear more for less.
In case of the suggestion from the opening post.In this situation:
Regular fur/leather: 2 point, 2 edge
Masterwork fur/leather: 2 point, 2 edge
Regular/masterwork cloth of all types: 1 point, 1 edge
Regular mail: 7 point, 10 edge
Masterwork mail: 9 point, 12 edge
Regular iron: 10 point, 12 edge
Masterwork iron: 12 point, 14 edge
This is what the mail set would have then:Skull: 26 point, 31 edge
Face: 14 point, 16 edge
Neck: 12 point, 15 edge
Shoulders: 20 point, 26 edge
Upper arms: 11 point, 14 edge
Elbows: 14 point, 16 edge
Arms: 6 point, 6 edge
Hands: 11 point, 14 edge
Chest: 11 point, 14 edge
Waist: 11 point, 14 edge
Hips: 24 point, 30 edge
Groin: 24 point, 30 edge
Thighs: 11 point, 14 edge
Knees: 11 point, 14 edge
Shins: 13 point, 16 edge
Feet: 5 point, 5 edge
This should hopefully make it clear what I meant when I said that overall buff to armor was not the intention. Even when mail is buffed to 9 point 12 edge at masterwork, the concurrent nerf to furs and leathers means that for the weight this still isn't really better than the current battlewear (though it would be better than the nerfed battlewear, which is the point). Much of the extra protection is again wasted on the already very heavily protected parts. The biggest benefit is probably that the face, neck and hands have now better possible protection. On the other hand the existing weak spot in feet is made more acute, while a new one is introduced in the forearms (needing either rare lamellar bracers or heavy double undershirt and fur overcoat to shore up). The torso is still worse protected.
It's not a problem of snowballing protection either from making the mail better. Both sets have lot that could be added to them, it's weight that determines how much can be added to either set.
In case of the minimal suggestion from my previous post.In this situation:
Regular fur/leather: 2 point, 2 edge
Masterwork fur/leather: 2 point, 2 edge
Regular/masterwork cloth of all types: 1 point, 1 edge
Regular mail: 6 point, 9 edge
Masterwork mail: 7 point, 10 edge
Iron is left as it is.
This is what the mail set would have then:Skull: 21 point, 26 edge
Face: 11 point, 13 edge
Neck: 10 point, 13 edge
Shoulders: 16 point, 22 edge
Upper arms: 9 point, 12 edge
Elbows: 11 point, 13 edge
Arms: 6 point, 6 edge
Hands: 9 point, 12 edge
Chest: 9 point, 12 edge
Waist: 9 point, 12 edge
Hips: 20 point, 26 edge
Groin: 20 point, 26 edge
Thighs: 9 point, 12 edge
Knees: 9 point, 12 edge
Shins: 11 point, 14 edge
Feet: 5 point, 5 edge
This is actually slightly weaker than the existing version of this set, so we are now talking about nerf to overall protection.
This is what the battlewear would have then:Skull: 21 point, 26 edge
Face: 11 point, 13 edge
Neck: 10 point, 13 edge
Shoulders: 13 point, 16 edge
Upper arms: 6 point, 6 edge
Elbows: 11 point, 13 edge
Arms: 8 point, 8 edge
Hands: 9 point, 12 edge
Chest: 8 point, 8 edge
Waist: 8 point, 8 edge
Hips: 12 point, 12 edge
Groin: 12 point, 12 edge
Thighs: 6 point, 6 edge
Knees: 15 point, 17 edge
Shins: 8 point, 8 edge
Feet: 5 point, 5 edge
This is worse than the mail set now. Even if you throw in the 10 pounds worth of clothes, it's not enough to shore up the differences. However I think it's worse to rather marginal degree in comparison to the mail set, and again masterwork body armor and leggings are very expensive and rare. Even if the base mail is limited to 6 point 9 edge, I'd still consider giving metal armor +2 bonus to both point and edge at masterwork.
It's also worth noting that in the minimalist scenario regular, rough and possibly fine mail would remain questionable as I pegged this at best possible protection.