AD&D1e: Abstractions work
Bill the Dungeon Delver does a regular livestream which you should subscribe to, and each week I join him to talk all things gaming. If you prefer video, watch - we get right into the guts of it from 22'40" in. This is the text version which is clearer but not as funny.
We talked about how AD&D1e's abstractions just work. You shouldn't mistake precision for accuracy. Just because it's detailed doesn't mean it's right, and just because it's abstract doesn't mean it's wrong. Armour Class and Hit Points are not precise, but they're accurate.
The first thing to say that all game rules must be subordinate to the referee's common sense. If a fighter in plate mail with 100 hit points is tied to an altar to the evil ape god Ollirog, the priest Thulsa Ook need not roll to hit or for damage, still less would they need to strike 30 or so times to sacrifice them to the hungry god. He's tied up and helpless, he will die. The wise player will endeavour to avoid the ever having to hear the blood-curdling cries of "ook! ook!" and finding the man-eating apes upon him. This discussion assumes the players and DM are not idiots, and we are discussing AC and HP in normal combats.
In science, accuracy means how close the measurement is to the true value; precision means how exact and reproducible the measurement is. For example, I am actually 1.78m tall. If you measure me 3 times and the values are 1.75341, 1.75343 and 1.75340m, then the measurement is precise but not accurate. If you measure 3 times and the values are 1.82, 1.76 and 1.78, the measurement is not precise, but it is accurate. Ideally we want both accuracy and precision, in practice it's hard to get both, and there are all sorts of techniques employed to correct for this.
It's a common tactic of sloppy journalists and unethical scientists (they're often friends) to confuse precision for accuracy. If we say that during a diet the average person's weight dropped 10.98438kg, this seems more credible to us than if we say "about 10kg." They hit you with precision to convince you of accuracy.
In roleplaying game design there are similar considerations and issues. Commonly game designers will bombard you with precision to convince you their system is accurate.
For example, GURPS has you account for every last gram of encumbrance, then asserts that the average person under ideal conditions can march 80km a day every day indefinitely, and can put 70kg overhead. It is precise, but not accurate.
Rolemaster gave us critical damage and fumble tables, so you had something like a 1 in 200 chance that when you fired your bow you'd lose an ear. By the end of the Battle of Agincourt the English longbowmen would not have any ears left. It is precise, but not accurate.
An abstract system like AD&D1e is imprecise - hit points, armour class, etc - abstractions, and abstractions are always imprecise - they're not exact, and they're not perfectly reproducible. The real question is whether it is accurate. I think it is.
Let's consider Armour Class. A common criticism of armour class is "armour doesn't make you harder to hit, it makes it harder for the hit to do damage", and this is true - but it comes to the same thing.
- Armour stops damage: Let's say your weapon does 4 points of damage, there is a 50% chance to hit someone and the armour will take away 50% of the damage - over several rounds of combat, 50% x 50% = 25% of the damage or 1 point will get through.
- Armour makes it harder for you to be hit: With the same weapon, we now give you a 25% chance of hitting someone, but the armour takes away none of the damage - over several rounds of combat, 25% of the damage or 1 point will get through.
- up and fighting unhindered
- fighting, but hindered in some way
- not fighting