I'm not certain that realism and balance are separate concerns. For instance, Omegaz brings up the analogous situation of monsters. Now, let's imagine that we're statting monsters up for "realism" without any concern for balance. We start with a housecat. We've seen cats fight and they have two front paws and a bite. They regularly use all of them, so we'll give them two claw attacks and a bite attack. A claw doesn't always do the same damage so it needs some kind of variability--we'll give it a die size that lets it do 1 or 2 points of damage after we figure the strength penalty in: 6 strength is -2 so they need a d4 claw damage. Their bite is more dangerous than the claw, so we'll give that a d6. Cats pounce much like their larger cousins so we'll give them pounce. They don't seem to have a lot of trouble hitting things despite their relative weakness so we'll give them weapon finesse so that they can use their dexterity instead. It's a realistic cat, right? Except that, given the stats for a human commoner, any housecat is about 50% likely to kill a grown man in six seconds. Well, I guess that's not too realistic then is it? The balance with other animals in the game as well as with people has to be preserved if we are going to say that our house cat stats are realistic because, in the long run, it's more realistic to have a housecat that can scratch a man but will have very little chance of winning a straight-up fight with a commoner than to have a housecat that uses two claw attacks and a bite attack.
The same thing applies to weapons. Let's say it's realistic that a historical falchion would deal more damage than a longsword but and would punch through armor more easily but would be harder to defend oneself against another foe with and would be less deadly against unarmored foes. Based on that set of stipulations, maybe we should give a falchion +1 to hit and damage against foes in heavy armor and -1 to hit and damage against foes in no armor. On top of that, we'll give a falchion wielder a -1 to AC. Damage die is d8.
Now, however, the falchion is more effective against armored foes than a heavy pick and a falchion wielder has more trouble defending himself against foes than the wielder of a battle axe. Furthermore, a character is better off wearing chain mail than the heavier and more effective banded mail when facing a falchion wielder. None of those situations are realistic.
Focusing on realism to the point of ignoring other game elements does not actually yield realism. (Nor does it yield good, playable game design as the 1e weapon vs. armor type table demonstrates).
