Mobs armor balance

Needs to be changed, i think. It touches melee chars mostly.
For example, at lvl 12 with vamp claw/str helm i can farm trolls (18 lvl), and it will be continued till lvl 30. Or even 36. Coz they have 0 armor. But at my 40 lvl i can't deal with melee centaurs (31 lvl mobs). Problem is in their 20 heavy armor :X. I prefer to kill lvl 100 acolyte (with some pots in invenory), coz they have 0 armor too.
Mages only win in this case, having extra spell dmg at heavy armor units.