It should go to notice that WOTC solved a lot of the barbarian class's disparity in the Playtest but not the fighter's,
Why?
Because the Barbarian is well defined whereas the Fighter is vague.
Because the Barbarian is well defined, WOTC could go "Wellwhen the barbarian rages it channels energies right. Usually its primal but it could be divine with a zealot or arcane with a wild soul. And sometimes its just anger and sweat. Well what if this anger lets the barbarian use their Strength modifier for some skill checks. And at high levels a barbarian is so strong that their muscles can't give aresultlower than their score. Because MUSCLES AND RAGE!"
Some might see it a bit weird but if you accepted the barbarian so far as the rage monster, a little more rage into noncombat is not the last straw and fits the archetype. The question becomes what is the DC to jump an extra 20 ft up?
But for the fighter, the fighter on just the nonmmagical side represents:
- The Brute: The strong tough and fast bruiser who focuses training on athleticism.
- The Knight: The strong warrior of a warrior caste/class/culture/country who masters the combat arts and cultural ideals of warriors of his heritage
- The Warlord: The general of the tactics and strategy who puts emphasis on the mental side of combat and the positioning of combatants.
- The Weaponmaster: The master of the very art of weapons combat and the technical and philosophical aspects of the duel
Each one of these fighter archetypes would handle high levels differently. A Brute would just jump at the flying dragon whereas the Warlord goads the dragon down with insults and Weaponmaster switches to a bow. A Knight might have skills in Diplomacy whereas the Brute might pull a barbarian and trade Cha for Str in Intimidation while the Warlord and Weaponmaster use Insight to give the Rogue hints into what words triggered responses in the cornered foe.
Because the fighter itself is not a family of honed archetypes like other classes, there is no single feature that could represent them all. And a subclass lacks the space to provide a substitute.
This displays how it breaks down at high levels. 14 Charisma and Animal Handling Proficiency might be enough to be a chivalrous mounted knight at level 5. But at level 15 not only is it not enough, others can copy that easily and it isn't enough to mimic epic knightly actions.