Berserk has a number listed after it, e.g. Berserk +3. The units get +3 to att and str and prot, but -3 in def, when it goes berserk. Berserked units will never retreat from battle, so they have morale of 99. Units that can go berserk, like Lava Warriors, or Arch Theurgs with Nature 6 blessing (
), won't go berserk before they are hurt in battle.
However, the armor's effect on defense is the more probable culprit in this case. Check Ulm; their heavy units can have defense 3 after armor/weapon maluses...
Weapons can also affect defense. Every weapon's defense affects the wielding creature's base defense - attack only affects attacks made with that weapon.
You'll be confused about mounted units' defense shortly; mounted units don't get defense penalties from armor, and get a slight bonus for being mounted.
You probably didn't need the exceptions, but here they are.