As a segway, on "realism". Historically human beings have been able to take quite a bit of firearms damage and still survive. Look at Black Beard the pirate and how many shots he took. Look also at something like the Black Hawk Down incident or Operation Viking Hammer, where people took multiple hits and kept fighting. This is a big garish, but even an untrained person like T-Pac took a gun shot wounds to the groin and the back of the head at close range and lived to tell about it.
Guns can kill a person with one shot...but sometimes people can take multiple wounds at keep going. The human body is weird.
It's not only being able to take a bullet. It's about increasing your ability to take more bullets.
Your character's pool of HP reflects his physical toughness, to be sure, but it also includes as its bulk abstractions of his ability to avoid meaningful damage from attacks.
That's solely an issue of game design. There is nothing requiring the exponential increasing of PC traits to be tied to increases of either class or character levels. They exist because a designer made a decision to arrange the rules to work that way.Yes, but that means that at level 1, maybe 1 out of 2 shots are grazes. At level 10, 19 out of 20 shots from the same shooter are grazes? With swords and magic, it's easier to handwave it. It feels right that a more skillful swordsman would be able to convert more attacks from a novice into grazes.
I just think that as technology gets involved, the basic concept of "levels" starts to break down. But I think that most people who play RPGs like the idea of levels, and prefer to play in settings where the concept of levels is less jarring.