I'm finding it difficult to know just what you're arguing for.
How are you going to take into account things like dosage, body weight, and so no?
IMHO you are just trying to obtain an unrealizable result in D&D.
In D&D high level characters can drink bottles of poisons without any negative effect, no matter their body weight, dosage etc.
Unfortunately in D&D even poisons aren't realistic at all, and are designed for unrealistic people.
In real life there are no Dark reaver powder, Purple worm poison or Dragon bile.
I think that's why El Mahdi was saying that HP worked fine for poison. One bonus of having an abstract HP system, is that it can take a lot of fine details of certain effects and make them abstract too. Drinking that poison didn't kill you? It must have been a lighter dose, or your body chemistry wasn't as affected by it, or maybe the saliva of that Chimera bite you took twenty minutes ago helped counteract the lethality of the poison.
And yes, most poison in the D&D are not real, but we can draw on real world poisons and draw parallels, and realize that not every drop of poison is instantly lethal.
Good luck to your PCs in any dungeon.
Are your dungeons really that filled with pools of acid? I think I've seen one pool in the entirety of my game play over 28 years.
But what about a PC trapped inside a closed room in fire?
What about them? They take continual fire damage until they escape or die, just like any regular person would. The only difference being that a hardened adventure may have the wherewithall to struggle to get out, rather than succumbing to smoke and pain as most normal people would.
How many Giant's club hits should a high level character be able to sustain before dying in your "realistic" scenario?
So your PCs are going to face deadly enemies 24/7 because they know they are incredibly lucky?
Isn't the same thing as jumping from 200' and knowing the impact will not kill you?
No, El Mahdi said that luck plays a part in things, just like in Real Life. HP loosely reflect this variability in life. There are countless cases of people taking what should be far beyond lethal hits and surviving ... multiple stab wounds, spikes through the eye, run over by cars, falling tremendous distances. And yet people have died from a single stab, or slipping on the floor and hitting their head. It's that fact that keeps us from running around willy-nilly and jumping off buildings. Sure, we know that one _can_ survive, but it's not assured, and so we logically don't risk it. Just like most people don't stand naked and unmoving in a fight. And in a fight, you're talking a humungous range of variables; dodging, parrying and deflecting blows, luck, attacker's skill, ability to roll with the hit, armour, and so on.
I think the desire for 'realistic' falling damage stems from the potential to meta-game. If you look off the side of a 100' building, you are probably going to think that there's no way you're going to survive jumping down, even if there are stories of people who have survived such falls. PCs should really be no different, but the game gives us knowledge of what will happen... 10d10, so 100 damage ... my 22nd level character can survive that, and we're resting soon, so wheeeee!
There are hundreds of lethal menaces in D&D.
Heck, even a large boulder falling onto an unaware human should squash him like a bug.
If it hits solidly, in just the right way, sure. Or it could cripple, or just pin the character, or maybe the character reacts instinctively to the sound of falling rock and danger from their years of adventuring to get out of the way in the nick of time. Not every falling boulder instantly and automatically hits a target below it.
Not to mention that, IMHO, a Masonry wall (1 ft. thick) should "survive" to many "attacks".
But in D&D such a wall has hardness 8 and 90 hps.
A high level barbarian has many more hps than a masonry wall.
A wall also cannot move, dodge, parry, threaten, and is unlikely to have much luck or divine intervention.
I don't want to imagine the real world consequences of being hit by a giant's club, anywhere on my body.
PCs who must face real world consequences would never face real world insurmountable menaces.
In real life no group of 4 people would ever face a colossal dragon, or anything of CR >4.
I think you're wrong in this regard ... people have and will continue to face real world menaces that some would regard as hopeless or insurmountable or extremely dangerous. Sure, not every single person, but there are those few who will find it within themselves to push on despite the odds. That's why the PCs do the things they do, because they have that drive in some form or another.
Real world people have gone up against fully armoured tanks with nothing more than a rifle and a bottle of flaming alcohol. A real world person stepped in front of a moving tank, not knowing for sure that it would actually stop. Real world people have gone into flaming buildings on the verge of collapse. Real world people do go after dangerous persons for rewards.
If there were D&D menaces in the real world, like dragons say, I am more than confident in betting that there would be real world people willing to try killing them.