I think attack is fine, and I think magic damage will be fine once the spells come in. the problem is defense. High dex and high armor are shoehorned together.
Borrowing f rom a MUD I play and an RPG system we used to use in school, I'd suggest the following rework.
You have two defenses.
Passive defense- means you dodge/parry/avoid blow completely. This is based off DEX mostly, with some modifications from spells, plate armor, abilitiies (like shield block, parry, etc)
Buily armor reduces dex percentage wise. This means that high dex chars are actually better off not wearing bulky armor potentially. Plate mail might be +6 PD, but -50% dex. Veteran troops might get a feat of platemail familiarity which would give +25% dex while wearing platemail. (to halve the penalty)
Damage resistance. This is determined by the armor+ skin toughness. This reduces damage of attacks linearally. 5 DR to an 8 attack will equal 3 damage, unless critical hit occurs. Critical hits ignore DR (but not PD). A peasant with a pointy stick might be able to poke a knight in the eye after all.
You could split DR up into crushing/slashing/piercing/magic. I don't think this is necessary though, and unsure if AI could handle this.