If you're trying to create compeletely realistic weapons, then you have to make everything else realistic as well. It won't work otherwise. It'd be just silly, being utterly realistic in one thing and unrealistic in other.
...No realism there means no realism anywhere. Either all must be realistic, or the whole thing must be ignored in favour of game mechanics and fun. Thus, no realism.
In any point of view I believe it is good to stay out of extremes. I don't see the game as completely unrealistic or do not want to make completely simulation-like one. What I mean is that people do reflect some reality to the point they are concerned or wish to, or skip some aspects, however they generally do not go the other way, purposely deform the way-things-are. To try to simulate everything completely it is not possible even in theory because there are still many unknown phenomena to our science. As I said to stay with common feel and implement things that actually matter in certain circumstances, like games.
You're just talking about some silly insignificant shotgun physics and forgetting all about the fact that, in real life, you will be dead or at least crippled anyway when shot once with any kind of a gun. What happens if you made it so, that you die from one or two shots, and if you don't be killed outright, you'll receive a serious decrease in hit chance, speed, dodge chance, among other things? People will complain. They won't like it.
I believe this thing is just what game requires since the beginning, because without it could be no game. IMO hit points represent things that cannot be
included with the game, like your combat sense, feelings, ability to act and think clearly under stress and while wounded, natural predisposition, etc., all that would make you last longer before getting killed. So hit points, from certain point of view, is like a time you have to react with game abilities to simulate/compensate lack of these natural qualities that cannot be included with the game.
..but ask yourself this, would making the game more realistic really make it more fun? Or take away what makes it Doom RL? Does it really matter whether something you play for entertainment is exactly like our reality or not? Some would say yes, others, like myself would say no. Ignorance is bliss. :O
I believe what is joyful about games is that they let you find yourself in some situations which are hard to happen in our normal lives. It means you find yourself, as if in this world or based on the laws you know and grown up with, in completely different situation that lets you act and do things normally not available. To do this you have to have feeling that things in the game correspond to our own, to some extend. If someone made everything non-sens you would not be interested because you would not understand anything.
And I don't think game should be "more realistic" - game is meant to be fun and balancing, if we start making it realistic we'll end up with marine beeing unable to go below first level or so because accumulated fhuman fire would quickly result in fatal wounds requreing medicial attantion beyond what so called "med-kits" can provide, while formers themeselves would have to be nigh impossible to kill (zombies - no need to breathe, no need for blood = 90% of shots would do nothing). Yes I'm probably pushing the example too far but from my experience forcibly trying to put realism in games that aren't mant to be ralistic brings only disaster.
Like in above post I believe that 'realism' is what lets you taste things as if you were in some kind of situation that is normally hard to come by.. To do that you don't need to simulate everything completely. Just what is essential, and lack of possibility of simulation can be replaced by some other means (like hit points). However making things work opposite takes that feel of experiencing things away.
If we make game in which marine dies on 1st or 2nd level, there would be no point of making this game. What makes sense to make, should be made, if something requires to be left alone then should be left alone. What I mean: we know that we can heal ourselves with medical aid. However it is different process. Because in-game we have health that works different way, medi-packs also work different way. However the essence of these two is the same. So with this we feel ok.
However if some things work against the laws we know, we start to question, because it doesn't work as it should.. And it is something we put aside and continue playing, but if it was up to us we would change it. Not everything should be altered for balance-sake. The trick is to keep it up with other things, not to keep up other things with the balance.