Overall, I feel the weights are wrong. They all seem on the heavy side. You wouldn’t see knights in plate if it weighed as much as 100 lbs. You may be thinking of the 16th century tournament armours, but no armour worn on the battlefield weighed 100 lbs. Given that throughout history, the average grunt has carried around 40lbs of equipment with him. Any more and he tires too quickly on the battlefield.
The prices you have suggested seem OK, given a silver standard, rater than a gold one. I also liked the separate chart for “recommended retail price”.
Compared to the PHB, your arcane spell failures are lower. Any particular reason?
The AC boost seems VERY low, especially when you compare to the amount of movement you loose, and the Dexterity loss. Interesting to see that the Flex armours retain High Dex.
Now given that a game with this much revisions to the armour system, I’d expect a lot of revisions in other areas as well (weapon damage, spells, feats, monster AC’s/abilities and so on) Why? Because it implies a creative DM! ;-)
However, let us look at what happens in some selected scenarios, all other things considered equal.
FS = Fighter Seasong (using seasong’s armour rules)
FG = Fighter Green (using PHB armour)
They both have the same BAB, feats and are in all respects equal, except for their armour. Neither use any magic whatsoever. They don’t really fight, just take damage (or avoid taking damage)
A hobbit armed with daggers attacks them both while they are wearing “plate” (full plate).
FS has AC 14 plus no DEX.
FG has AC 18 plus up to 1 DEX.
FS gets hit 20-25% more often, but takes no damage, unless the hobbit has a Strength score, sneak attacks or should score a crit.
FG gets hit more seldomly, but takes more damage.
Is this good or bad? That is a matter of opinion.
IF the aggressor is a Giant armed with a Huge Great sword and using 3.5 E power attack, FS is going to get pasted, because the DR does not make up for the lack of AC:
(assume wimpy 24 Strength giant)
2d8+10 +PA –4 = 2d8+6+PA= 15+PA hp on average, * 120 % = 18 hp +1.2*PA
2d8+10 +PA = 19 +PA hp on average
And crits are more likely to get confirmed against FS.
This gets more noticeable as the damage dealt increases.
Now Seasong’s armour is less likely to be min-maxed than the core rules (as PHB is fairly easy). After some careful thought I see Mail or Segmented Plate (at low level) as being the dominant armour of adventurers:
For Mail, although the Damage reduction is relatively low, the Arcance Failure is clearly “best in class”. Secondly the high DEX means that it will be usefully for many types; Rogues until 10th level, Dex fighters, Rangers. My point being, there are not many ways to increase AC, so having a good combination of AC + Dex + DR means that Mail will be one of the top armours. (AC19 +DR 2/-
For Segmented Plate, this is obviously the best armour for low level tanks: 14 in Dex is possible through careful point buy, even for a tank. AC 16 DR 3/-. This will give way to Scale as players migrate up their Dex through item acquisition. AC 17 DR 3/-
Summary
I can’t see a 1 increase in DR to be worth a 2 drop in AC, given the large amount of large creatures that deal huge amounts of damage, especially later in the game. This is especially dangerous to the tanks given that Crits are much more likely to get confirmed, and they are the people most likely to suffer criticals as they are always at the forefront of the fight.
Given this, these changes lead to the extinction of the tank to delight of the Dex Fighter. Or the detriment of the party as a whole.
Lonesome thought
While Mail is probably a more practical armour to go adventuring in, I find it sad that it should become regarded as the epitome of armours on the battlefield.