You're assuming they get shot. I've never assumed a "hit" in D&D does direct physical damage. When it comes to firearms, it's a grazing wound, a bruise but your armor stopped the bullet, a bit of shrapnel from the bullet that hits the wall, it's the pulled muscle as you leap out of the way as you see someone pointing a gun at you, it's luck and plot armor.
Realism and games don't often mix. That's not just D&D, that's all games whether TTRPGs or video.
Sure, but the d20 Modern rules don't really
allow your interpretation to be correct, because rider effects from attacks land when attacks land - like poison, being set on fire, damage multiplication against certain types, or stun, or even impalement. And a lot of characters in that either don't wear armour or barely do. If you get set on fire by a shot, you can't exactly claim you "pulled a muscle" or something lol.
If you have a game that totally avoids riders, or makes all riders into vague things open to interpretation - and there are games like that - that works. But not with d20 Modern.
You end with what I'd call a "Tintin" situation - which is essentially a farce. Someone keeps getting shot and every single time it's "just a graze". It's just like how Tintin is frequently shot in the head, and it's always "just a graze", and at some point, that stops being remotely believable, even as an "action movie" thing and becomes clearly a farce.
I think what maybe you're not really looking at here is that, any individual shot, you can probably, if you work hard enough (and it can be hard work) justify how this hit for 22 damage which also poisoned you, was "not really a hit", and in D&D that works. But you keep doing that, long enough in, say d20 Modern, and I dunno - you might be fine - but my experienced crew of long time D&D players? They weren't fine. And from discussions of d20 Modern, a lot of other people who were fine with in D&D just found it over the top in d20 Modern.