Ok had a nice long post just go *poof* before my eyes. So I'm gonna type it out again, but it is doubtful it will contain the eloquence and thoroughness of the original post...but hopefully I can recall all of the salient points.
The Fighter is an interesting case (in this context), because its subclasses are more mechanically driven...in a more "thematic" [?] or, even, "abstract" sense than the other classes' archetypal and/or flavor driven options. Instead of a Samurai subclass and a Warlord subclass, we have a Battlemaster. Instead of a Gladiator subclass and a Swordsman subclass, we have a Champion. Even generic non-TTRPG derivatives like "Defender" or "Leader" are subsumed into these more broadly generic subclasses.
The fighter's options don't offer the specified...flavor, I guess, of Illusionist wizards or "Wildshaper" druids...or even Assassin or Arcane Trickster rogues -who, we can presume, were intended to be the same as/match up with the Fighter's options: generic guy, specialized/slightly more complex guy, guy with a little [1/3rd caster] magic.
So, a lot of the declarations presented in this thread really don't hold up in the Fighter's design space.
We have the generic "hit harder/more often" warrior guy, no bells, no whistles, swings a sword, rolls his damage: the Champion.
We have the less generic/more specialized, slightly more complex to run/more moving parts warrior: the Battlemaster.
We have the warrior + [a dash of] magic [1/3rd caster, since 1/2 casters get their own classes], who uses both -fluidly- in battle:" the Eldritch Knight.
"We need a Samurai!" The Battlemaster, quite obviously, is intended to give you a samurai. They've already said the long sword [being a versatile weapon in 5e] is the same as/can be easily swapped out as/for a "katana." Put the fighter in some traditional samurai-style armor (wherever you would get such a thing on your world). The BM's artistic talent feature is blatantly intended to give you that traditional samurai calligraphy/painting training. It's all right there. We have a samurai already. Unless you're looking for "Language: Feudal Era Japanese" on your character sheet, there really isn't anything to do here. They could, reasonably, add a few "martial arts" or "samurai moves" style maneuvers to the BM's list, but it certainly doesn't warrant its own subclass.
"We need a Defender!" The Champion is your defender. Roll up a Champion, put them in the heaviest armor you can find, give them the Defense or Protection fighting style (and take both at 10th level). Speak softly and carry a big shield. There's a "defender" fighter.
"We need a Warlord!" See "samurai" above. It's all there. The helping others and "rallying" maneuvers, the knowing about your enemies, everything you need for a non-magical warlord PC is in the Battlemaster. If you want more healing, group support magic, "inspirational leader" guy, there are Bard subclass options for that. They're handing out Inspirational help to your rolls like hotcakes.
"We need a Gladiator!" The Champion or BM could serve as your gladiator. Honestly, it strikes me as more in line with a 5e Background than a subclass...folks from anywhere, all over, even non-fighters could be wrapped up [enslaved] into the role of gladiator...hell even a fighter or barbarian with the Entertainer background could be a Gladiator.
The one I have seen, that I could totally see, highly approve/agree with, and it makes sense [as well as symmetry] is a 1/3rd caster of clerical/"divine" magic to bookend the Eldritch Knight's "arcane" magic. I think "Crusader" (as others have said) is a PERFECT title for such a character and falls in line with the Fighter's design frame: 1/3rd caster [of divine magic] and it works for an array of character types from the old school "Fighter/Clerics" to a "mercenary fighter with a holy streak, but not so devout as to become a paladin" and lots in between.
So, if I'm getting my point across, what we need is another, if there is to be another/different Fighter subclass, is something that is a different mechanic to fight with. I am not a fan of just making/spamming more "magic types." I think the Fighter [and Rogue and Barbarian] should be predominantly, overwhelmingly, non-magical characters. But something that, I suppose, makes the Fighter even more complex/moving parts than the BM. Or simply a different mechanic for determining damage...or attack accuracy...or something.
What, I think, people are looking for in the Fighter, isn't [or shouldn't be] so much new subclasses, which I am sure they think they do, because it just seems more "official" [I guess] that way...But new Fighting Styles, specially/specifically-flavored Battlemaster maneuvers, and character Backgrounds. Those are the moving pieces that can turn your "Champion" or "Battlemaster" into a hundred different things. If you want new Fighter subclasses, we need new moving parts -entirely- to work with.