steeldragons
Steeliest of the dragons
That's not quite true. In AD&D and BD&D, fighters were feudal lords.
Hey there, old bean. Been a while! Nice to "see" you again.
I will take issue with this assertion.

Fighters were not "feudal lords." They were guys who fight...who, maybe, after however many levels, might build a stronghold and, yes, attract followers and mercenaries and the like. Like everyone else.
I believe in BECM (at the "C" point) you were, literally, just given/made a "Baron" but who was really playing BECMI at "C"? Dwarves, Elves, and Halflings all also became "lords" among their people. Clerics could build strongholds and attracted followers too (who didn't have to be paid, no less! iirc) Thieves got their hideouts and mages their towers with limited followers/apprentices.
At least that was the narrative built into the mechanics as they leveled up. Other classes of the era did get followers, but not to the size and extent of the fighter who amassed an army. 3e marked a departure from that assumption, and that departure continued in 4e, and now in 5e. Nothing wrong with that – many modern players don't want to play feudal lords – but removing that bit of identity left a vacuum.
But there wasn't really ever a "I'm going to be a fighter because I want to be a feudal lord/that's the lord-class" built in to the class. Strongholds and followers were an automatic part of both B- & AD&D...for almost all classes. Certainly all of the original "big 4" [or "big 7" if you are talking Basic and count the demihumans]
3e tried to fill that vacuum with a huge assortment of prestige classes & feats.
4e tried to partly filled that vacuum by making all fighters Those Who Defend Others.
5e tries to partly fill that vacuum with backgrounds.
Yes. I get the argument you're trying to make. I simply disagree with the premise. The Fighter had no "void" to fill. Certainly not by losing what every other class was getting [some version of] as well.
I agree that Mike Mearls is on the right track that the fighter subclasses are a good place to provide identity (identity-as-a-tool-like-other-classes NOT identity-as-a-straightjacket).
I don't disagree, here. And making subclasses based on flavor are certainly easier (and more fun

Where you see absolute truth, I see self-fulfilling prophecy.![]()
As is generally the way.

Back when I read the AD&D2e PHB as a boy, I remember reading about figures from literature, history, and myth that the fighter class was inspired by: Hercules, Perseus, Hiawatha, Beowulf, Siegfried, Cuchulain, Little John, Tristan, and Sinbad. El Cid, Hannibal, Alexander the Great, Charlemagne, Spartacus, Richard the Lionheart, and Belisarius. Many of these men (and yeah they were all men sadly) were very charismatic, they were renowned, and people followed them. Many were also masterful tacticians. And most came from cultures with a warrior tradition.
Yes. I'm not sure I see what you're saying here. This is precisely what I am asserting. The Fighter class IS supposed to be any/all of these characters (and many more).
My thought-experiment for anyone subscribing to "The Fighter Fights" theory is imagine the class was named "The Warrior" – it wouldn't make sense to say "The Warrior Wars", would it? A simple name change invites us, as designers & players/DMs, to wonder what it means to be a warrior, and (hopefully) makes us ponder the nature of a warrior when it comes to game moments, and not just those involving swinging swords.
Alright...ya know I enjoy a thought-experiment.
So...(and in answer to your query above, yes, it would, actually, make sense to say "a Warrior Wars." That's precisely what that means. But anyway, I'm happy with...) "A Warrior fights." That is their purpose. Whether it is for defense or conquest or glory or cash is immaterial. They fight...otherwise, what kind of warrior are they?
So, "The Warrior" class needs to be able to attack and deal damage effectively. Be able to attack, with weapons, more often and/or for more damage than other classes. Extra Attacks and Fighting Styles seems to have these bases covered. Granted, however, that farming these out to Pally's and Rangers, as well as Barb's and Monks getting Extra Attacks as well, makes all of that seem significantly less "Fighter-special/specific."
The "Warrior" need to be able to "take a hit." They need to be able to maintain and withstand a prolonged conflict when other classes would need to end/submit or retreat [or die]. Their higher HD and the Second Wind feature seem to have covered this base.
Given that the Warrior is a class dependent on their use of arms and their physical strength, then some measure of ability with their physique seems appropriate. I am amazed that it took us 8 [or 10 depending on who you ask] iterations and editions to end up with something like "Remarkable Athlete" and I think that type of feature suits the [base] Fighter-Warrior class beautifully.
It all seems fairly self-evident...and what we have already been presented with in the PHB.
My own homebrewed system's Fighter class (and I have wrestled with shifting the class name to Warrior, myself, many many times) includes a low level feature that provides interaction bonuses with other warrior types (of similar disposition/alignment) and warrior/battle-dominant cultures that are of lower level than the PC, "Veteran's Camaraderie." Basically, my thinking was, warriors are going to have a degree of implicit or explicit respect for other "brothers-in-arms." Those who have seen the horrors of war and know the ways of the battlefield. Ya know...how Jocks and Military Guys are [often] with each other IRL. So a minor bonus to interaction rolls didn't seem out of place...and wasn't a "combat-related feature" thing.
I guess that's all I've got in the thought experiment for now...whether "Warrior" or "Fighter" or "Wielder of the Sharp & Pointy."