As much as I love my Barbarian, I dont think it needs its own class - its a fighter with Rage and Reckless Attack feats
You can't have Action Surge + Second Wind + Fighting Style and Rage + Reckless Attack.
Just like the cleric and druid are 2 different classes because of Channel Divinity + Wildshape, fighter and barbarian (and monk because of Martial Arts + ki). because of mechanics. That's literally it. Mechanics. The classic classes flavor doesn't match the mechanics of the archetype. So you have to make a whole new class.
You can't make a Rage mechanics with the fighter: so we made a barbarian class.
You can't make a Martial Arts mechanics with the fighter: so we made a monk class.
And before you say "Make it a subclass", you can't with the "So simple and easy designed to be playable when your brain is shut off" Champion is a Fighter subclass. You can't balance Rage with "Improved Critical". We can't even balance it with Eldritch Knight's spells and Battlemaster's maneuvers.
This is why I predict the Barbraian will actually get bigger number to have more design space.