I think if the fighter's niche was pushed a little to include the '' spell less specialized monster slayer'', this would give it more thematic oomph, and then the ranger with spells could lean harder into the 4e Warden side of it, channeling nature to defend nature or the borderland folx.
The "subclass" model works better, however.
Have Class, Subclass, Archetype.
Class: Fighter
Subclass: Barbarian/Ranger/Paladin/Paragon/Weaponmaster
Archetype: Subclass specific.
Put more meat into Subclass.
Class: Trickster
Subclass: Rogue/Monk/Bard
Archetype: Subclass specific
Class: Magic-User
Subclass: Wizard/Sorcerer/Warlock/Artificer
Archetype: Subclass specific
Class: Priest
Subclass: Cleric/Druid/Shaman
Archetype: Subclass specific
The "class" here ends up looking a bit like a 4e power source.
Fighter
Fighters are at home on the front lines of combat. Tough, resourceful and deadly.
Tier 1: Tier 1 Fighters gain Fighting Styles and Second Wind
Tier 2: Tier 2 Fighters gain Extra Attack and Indomidable (reroll some saves)
Tier 3: Tier 3 Fighters gain Weapon Mastery (extra set of weapon damage dice) and Legendary Resistances (Indomidable now auto-succeeds)
The Paladin subclass might make the Weapon Mastery damage radiant, as an example of how the subclasses would modify base class features.
On top of it, the Paladin subclass would add spellcasting. The Weaponmaster subclass might add weapon specific features and abilities. The Paragon might add Battlemaster maneuvers, or might be the "simple" class with some extra static bonuses.
As a sketch:
Tricksters:
Tier 1: Tier 1 Tricksters gain Mobility and Expertise
Tier 2: Tier 2 Tricksters gain Sudden Strike (reaction attack) and Tumble (like the rogue 1/2 damage ability)
Tier 3: Tier 3 Tricksters gain Disable (stunning strike ish) and Reliable Talent
Magic-Users
Tier 1: Tier 1 Magic-Users gain Spellcasting and Familiars
Tier 2: Tier 2 Magic-Users gain Focus and Wards
Tier 3: Tier 3 Magic-Users gain Arcanum and Refuge
Priests
Tier 1: Tier 1 Priests gain Channel and Blessing
Tier 2: Tier 2 Priests gain Sanctuary and Smite
Tier 3: Tier 3 Priests gain Intervention and Incarnation