A perhaps divisive assertation: The use of hit points has always been one of the chief stumbling blocks between D&D and true genre emulation. They’re a rough and ready way to make combat something that is desirable rather than extremely risky (as it often is in systems that attempt to model health more realistically), but fantasy isn’t exactly full of statements like, “Aragorn saw that the orcs were wielding swords, so he knew he could withstand at least three blows, even with their strength, before his life would be in jeopardy.” Particularly at the rate hit points inflate as you increase in level, the use of them tends to either force you to use them as a complete abstraction or bend heavily the physics of your world. I’m thinking, in particular, of a scene a module I’m running expected me to narrate where a luminary that’s known to be at least of mid level doesn’t die when struck with a crossbow fired by a non-assassin attacker, and that’s supposed to be surprising to the players.
The classic attempt to have one’s cake and eat it too is to consider hit points to mostly be an abstraction of not only health, but agility and luck as well. That is, high level characters aren’t necessarily much tougher than lower level characters, but they’re much better at getting out of the way of attacks and turning a serious blow into a negligible one. The classic argument against this tactic is that it still doesn’t account for why a Cure Light Wounds spell that can bring a first level character from the brink of death to full health can only salve a few scratches on a high level character. However, that moves the genre emulation stumbling blocks to the healing spells, so in my mind it’s not a problem inherent to considering HP to represent ability to avoid or reduce damage.
Instead, my new concern is the attack roll. If HP represent, in large part, getting out of the way of an attack or otherwise reducing it to harmlessness, what’s AC? Isn’t it a little redundant to score a lucky hit against an elusive (high AC) opponent only to describe that he still dodged most of the way out of the way, only this time it cost him something? Straight up damage reduction is one of the hardest things to get in the game, but To Hit vs. AC is effectively a total DR that has a random chance to fire every round. Could we, in fact, make combat somewhat less swingy if we eliminated the attack roll entirely and moved its rules elements directly into the damage system?
Obviously, doing this to D&D itself is a bear of a project with a whole periphery of externalities to handle even if you could find players that don’t balk because they dislike such sweeping revisions to D&D. However, consider a system designed from the ground up to have only a damage roll: characters always “hit,” with the actual effects of such a hit managed by the hit point system (as opposed to a lot of non-HP systems that add attack MoS to a flat damage number and functionally have only an attack roll). In a straight up fight, eventually an opponent gets worn out from dodging/blocking and is struck by a vital hit, or is gradually worn down as powerful hits connect lightly.
In my mind, the benefit of such a system is that it allows a steeply-inflating “HP” pool with a more realistic set of wounds that can be used to represent real damage and be taken by attrition or surprise attack (similar to the Star Wars d20 Vitality system). It also reduces the chance that bad rolls or high defenses will make it feel like no progress is being made (as even a bad roll will generally take away a few points of the HP pool).
My major question is whether the complexity and time saved by going to a single-roll solution justifies increasing complexity on the division of damage. To wit, is it worthwhile to implement dodge and armor traits that establish how much damage can go to the HP pool vs. rolling over onto the core wounds?