It's not about realismn, but about things like believability and verisimilitude.
But actually, I don't think it helps.
It is believable that a man can fight a Dragon 10 times his size capable of breathing fire? Where's your verisimilitude here?
The only explanation that works is that this is a heroic character, way beyond what a real mortal can do. What such a man can do or can take, we can't relive in our real life.
Whatever hit points represent in D&D, they are most likely barely related to your physical body. They must represent a mix of heroic skill and stamina, divine luck, something that no one in real life has.
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There are things where believability are important.
People act according to human nature. They love, they hate, they make mistakes, they are corruptible, they are brave, or they are cowards.
Societies work as you would expect them to work from our history and present - someone is in charge, be it by vote, by divine right, or by heritage. Someone is serving them.
There are tribes, clans, families, kingdoms, empires and republics. There are cops & robbers. There are loyalists and separatists. There are traitors and those giving their life for their home or country. There are the rich and the poor. There are traders, merchants, artisans, soldiers, mercenaries, peasants and slaves.
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And if I may say, I think D&D sometimes feels in this regard.
A society of chaotic evils where everyone is out to kill his superior? When did such a violent society ever exist, and could work for long, and be considered as a strong power? A society where you can only advance if you kill all your "equals" in your area of expertise?
Political back-stabbing is one thing, but physical back-stabbing is quite another. (Yes, I am talking mostly about Drow.)