I’m not sure I see the problem other than – as per usual – definitions and expectations. To me, the Class is what is important, and the Sub-classes should be there to provide a tweak on how those abilities are implemented/focused on. This doesn’t need a dozen abilities tied to it, or basically you’re just making a whole class. What they almost all do successfully is add in a new mechanic, or an adjustment on the existing mechanics that’s key to the class….
So Barbarian = Tanks while Raging, Berserker = Hits more while Raging, Totem = More flexible/defensive while raging
Bard = Cast Spells & Inspires, Lore Bard = Distract & get more spells, Valour Bard = Stabby Bard
Cleric = Cast spells & Destroy Undead, Domains = Access different Spells and do 1 other cool thing
Druid = Shapeshift & Cast, Land Durid = Cast More Spells, Moon Druid = Awesome Shapeshifter
Fighter = hit things with weapons, Champion = Hit things Better, Battlemaster = Hit things stylishly, Eldrich knight = Hit things and burn them
Monk = Move fast and makem attacks, Open Hand = Hit Things Well, Shadow = hit things & Hide, Four Elements = hit and burn things
Paladin = Smite stuff and be immune, Devotion = Smite & Immune better, Ancient = Tank and Control, Vengance = Smite one enemy
Ranger = Hit, track and Travel, Hunter = Fight better, Beast Master = Fight with a pet
Rogue = Sneak about, Thief = Sneak & Steal, Assassin = Alpha Strike, Arcane Trickster = sneaky mage
Sorceror = Cast powerful Spells, Draconic = Cast spells as a dragon, Wild = Random spell fun
Warlock = Blast stuff, Archfey = Blast & Confuse, Fiend = Burn & survive, Old One = Blasty hypnotist
Wizard = Cast all the Spells, Schools = Cast types of spells better and gain spell like benefit
Most of those rough (very very rough….and subjective) definitions each have an early mechanic that applies to the main class identity and twists it slightly. Personally, I’m not looking for anything wildly different within a class – as that would require a different class altogether.
To take the simplest of examples – the fighter – and compare Champion to Battle master. A Battlemaster gains flashy moves, a Champion just hits harder with more weapons. One adds a minor mechanic (Superiority Dice), the other tweaks the existing dice roll (Improved Crit). Very simple concept.
If you added, say, another layer to each (Champion gets additional rerolls, bonus attack damage, big resistances, skills to frighten and the Battlemaster gained support and buffing abilities, intimidation, targeting certain enemies), it’s starting to feel less like the core fighter, and more like a sort of fighter/barbarian or fighter Paladin, or fighter Cleric hybrid. The subclass has moved significantly away from the core class.
But as I said at the top, this is what my expectation is from a subclass. I would argue the starting point for this discussion would be sifting out people like me who want something from subclasses very different from what you want.