You don't need to man-splain biology to us, dude.
No idea what man-splain is.
We know D&D HP and damage isn't realistic.
Yet, then the rest of the post (and several others in other areas) begs the question that HP are indeed traumatic soft tissue injuries and then asserts what they are not. Better yet, the "what they are not" you assert is precisely what they are and truly the only consistent thing they've ever been; "heroic staying power" and, by proxy of that, "the measure of a character's ability to sustain combat effectiveness". HP are the deepest of abstractions possible to facilitate TTRPG play that doesn't require considerable mental overhead, intentionally not equating to anything remotely resembling/acting as a representation of a biological system. As "heroic vitality", in the genre sense, it does the trick well enough if you squint and treat the narrative with a fortune in the middle coat of paint as you play out your scenes. And those are its intentions.
As has been done dozens and dozens and dozens of times before, we can go through the history of the game and the designer statements. From the fact that its inception is as the unit representing a ships' staying power in naval wargaming, which then was ported to Chainmail for miniature/combat unit wargaming. From its porting over to D&D and Gygax's mockery of the interpretation of HP as anything resembling the ablation of soft tissue rather than the measure of "heroic staying power" as was intended...and telling you that there are "competing" systems out there attempting these sorts of things so go to them if that is what you're looking for (which people did). From Dragon 39 which took a (I believe 1st) shot at visceral crits and silly fumbles (because the HP system doesn't try to support anything like it). From AD&D Combat and Tactics by Rich Baker and Skip William, where in their introductory and later, they again restate that "At its most basic level, the AD&D combat system is a contest of attrition that all boils down to who runs out of hit points first." Then they go about speaking as to how the idea of wounds by themselves in the system as written are absurd...but here is lesser wobbly crit hit and wound module to tack on to the system to supplant the much more wobbly one provided by Dragon! To 3.x, trying to tighten it up and break out a few components (such as "nonlethal damage" and some component parts of AC) but still (mostly) holding to the same old squishy definitions of HP and HP damage. To 3.x Unearthed Arcana realizing the system doesn't remotely even attempt legitimate process simulation or HP as meat so it gives you a WP/VP and armor as DR module. To 4e again reiterating that HPs are all the squishy, low-resolution bits of "heroic staying power" that Gygax and the rest asserted they were (and how they interact with the system), allowing each table to figure out what that meant in the fiction.
But HP isn't reduced when you do strenuous tasks...
No character ever died of being too tired...
What? This cannot be serious. My guess is that you started playing the game at 3.x but even there, the exploration rules of the system are rife with "HP reduced due to strenuous tasks" and "characters dying of being too tired."
Environmental exposure charges nonlethal damage galore. Nonlethal damage added to a character doesn't subtract directly from HP pool but it 100 % does reduce the available HP pool (and thus their heroic staying power) for heroes (so basically reducing it by proxy) when they have to deal with subsequent dangers. When those nonlethal HPs exceed your current, you're unconscious and helpless. Suffocation eats away HP. Environmental exposure to heat and cold accrue nonlethal and then lethal damage after they're out. Psychic damage eats away HP. Drowning eats away HP. Starvation and Thirst renders unrecoverable nonlethal damage and triggers the fatigued condition (which is triggered by several other environmental aspects).
Lets talk about the fatigued condition that doesn't kill you. Fatigued hampers your ability to survive the environment and win in battle. Exhausted
utterly cripples it.
People in real life die from "being too tired" all the bleedin time. Character's in a 3.x game die from "being too tired."
Historically, Evasion and Pursuit rules are lethal. From Gygax's squishy section which basically amounts to "you must figure this out yourself but it should slow movement and reduce combat effectiveness in proportion to your fatigue/exposure", all the way to 5e's Exhaustion rules which (a) render disadvantage, (b) inhibit > utterly end movement, (c) HP loss > to 0 (d) death.
Show one other example of HP being treated as stamina.
I've shown several. They're everywhere in the history of D&D. 4e treats this as Healing Surge ablation (and then HPs when you're out of Surges). All HP are is "metagame stamina" and, by extension, whatever you want them to be (including real stamina) in the fiction at your table. I've run it for almost 6 years and the number of Healing Surges (and then HPs after they're tapped out of HS) my players have lost over the years due to environmental exposure, emotional hits to morale, and/or mental and physical stamina is in the thousands.
I've killed players in all editions from the rigours, hazards and exposure of perilous journeys in every single edition, taxing them HP, having them accrue nonlethal HP, and rendering fatigue and exhaustion (including the AD&D C&T rules for fatigue and exhaustion) unto them and basically making encounters unmanagable by proxy; hence dead PCs.
My only point above was that it is morbidly absurd to try to shoehorn HPs as soft tissue damage and then decry people (and a system) for being irrational when they assume that a Fighter can recover his HP due to the sheer weight of his own grit and indomitable will (Second Wind) in the classic rally or heroic comeback (real life and genre).
And I've never been confused about what "to hit" means (it is metagame jargon meaning "to hit target number") and, given that + the incoherency of AC, I've never thought that when an Elder Air Elemental and the Tarrasque (or an unarmored, nimble swashbuckler and a heavily armored knight) are tangled in a deadly martial exchange, that every time the Tarrasque successfully achieves his target number "to hit", that a collision between the Tarrasque's exoskeletal fists/class/horns (whatever) and the Elder Air Elemental's "as dextrous as the very wind" "whatever its form is made of" is ocurring and thus being "hacked away" (whatever that would mean). Especially given that the outrageously slow/plodding Tarrasque would "hit" the very incarnation of fast/nimble several times over more often than the Elder Air Elemental would "hit" the Tarrasque.
TLDR; 5e Fighter Second WInd is just fine, especially when compared to the, self-admitted, abstract/incoherent (but awesome!) legacy that is the D&D mechanical chassis.
