My points is that hit points are intrinsically linked to the question of tactics in the gameplay.
Sure. Focus fire is the obvious example - hp damage imposes no penalties, so, focusing on one enemy at a time is always the best tactic, and accepting hp damage in return for enabling some other objective is often a pretty easy choice.
That is, you can always skip minding cover if all you stand to lose is a couple of hit points. Yes, in the long run you can't afford to lose hp carelessly, but skipping cover is a definite choice to weigh against getting to your destination quicker.
Nod. That kind of pedantic player calculation, though, actually can enable a genre-appropriate action on the part of the hero - apparent 'risk taking' or 'bravery' (the /player/ know the PC will just lose some hps - but lose some hps, in the fiction, looks like taking a deadly risk and barely getting away with it).
PS. As always, that doesn't mean there's anything wrong with using hit points for a gunpowder game.
I'm only trying to bridge two different viewpoints by explaining why resistance against hit points have real solid origins, rather than it being just "wrong"
In that sense there's no 'wrong' just inconsistent. It's inconsistent to get exercised about hp loss not being a sufficient disincentive against breaking cover in a western, but not about it not being a sufficient disincentive to say, charging a horde of orcs in fantasy.
Hit points are a very abstract mechanic, and can be used a lot of different ways to enable a lot of pretty cool in-game narratives. But there's a habit of thinking of them in a much more narrow, and internally inconsistent way.
But remember you don't need to reinvent the wheel here. The problem has been tackled before. You know, by other games.
And that's irrelevant to the topic at hand, which is using D&D in other genres, not converting D&Ders to other systems that aren't as bad as it at a given genre.
But do you really need to? I think the thing that bothers me most about this "D&D doesn't work with guns" is that unless you assume fully automatic weapons and an unlimited ammo supply, guns are really all that much different in game terms than what we already have. Particularly if you limit to 19th century or earlier tech, they really aren't all that much more effective.
One reason I have for the opinion that D&D can work fine with firearms - to that point, is that I've done and seen it done a lot the last, oh, going on 10 years, now, I guess.
For instance, back in 2010, I started playing in a campaign that brought PCs together from alternate worlds. I chose to pay a Cleric who was an Old-west fire & brimstone preacher. He didn't happen to be carrying a gun when he got sucked into the campaign's setting, so it was a non-issue. Later, closer to Paragon, the story worked around to an old-west world (with a zombie apocalypse), and we picked up a Ranger (who was literally a Texas Ranger), using a re-skinned superior crossbow with increased-RoF-feats as his Winchester.
Introduce firearms to D&D without a hitch a few times, and you start to get over the dogmatic horror of the idea that was the norm back in the day.