A person who is skilled in light armours and deflecting is able to move quickly and dodge more attacks than someone wearing heavier armour. If a person in this situation gets hit there is a good chance they will be hit very hard or just die outright. If you are lucky you can deflect a heavy blow to be a less hard blow and that is why learning deflect and being able to deflect is important for light armour wearers. This armour is weak to every kind of weapon.
A person who is skilled in medium armours can usually move pretty quickly still and can take quite a bit more damage than someone who was wearing lighter armours. This armour type is still weak to every kind of weapon.
A person who is skilled in heavy armours trades mobility for a very good defence against slashing weapons and attacks. A heavy armour user is still susceptible to axes, thrusting attacks of any kind, and blunt weapons (spear,morning-star,club,etc). Heavy armour wearers cannot move as easily, get tired faster and cannot flickup if knocked down.
At the highest level of killmode melee combat, it almost -never- comes down to who gets tired first. Fights at the highest level usually last until someone gets mortally injured (usually a critical hit causing massive bloodloss and damage) and cannot continue to fight effectively. It is worth noting that the more injured/tired/drained you become the worse you fight.
One exception to this that I have experienced is when a human or similar race fights a tshahark. If the two are of equal skill, the tshahark usually wins everytime unless the human(or other race) uses a shield and then they can usually wittle the tshahark down with small blows.
Strength is a -huge- factor in killmode melee combat. This is because the more strength you have the more ability you have to end the fight immediately with a huge critical hit.
At the highest level of stunmode melee combat, it is more of a slugfest. Some fighters can even come back to win from deaths door, though it is rare.
Melee combat has a few additional factors like, missile attacks, special thief skills, using throwable potions, retreating and re-engaging, etc. Combat and tactics are quite deep in this game.
Unless you are fighting a cleric, then they just lock you in an area with the silly "trap miracle" and miracle you to death.
The right man in the wrong place can make all the difference in the world.