As a random idea popping into my head that hasn't had a second of critical thought applied to it, what if everyone had a dodge bonus to AC equal to their BaB?
Or remove BAB altogether, and keep AC bonuses low, resulting in a very predictable chance of hit.
More emphasis could then be placed on soak.
Tetsubo: Two types, then? Deflect (AC bonus) and Absorb (damage resistance).
You can stack the two types together but not with their own.
For instance, character sports Padding (DR 2 or so) and wears some random Steel Plate covers (AC +3).
They find Chain shirt with sleeves, which grants DR 5. If they wear Chain it overrides Padding but the Steel Plate DR still works normally.
Likewise, other found or purchased Deflect parts could be bone, wood, ceramic, held shield, etc.
Absorb includes body fur, scales, cloth, chain, bulky muscle, and so on.