As a proponent of Barbarians as a class, I agree that the Berserker would be a great Fighter subclass.
Then allow the Barbarian to fully embrace the primal warrior theme it had in 4e and mostly has in 5e.
They’re canonically fully sapient, and possessed of free will in a non-deterministic universe (dnd assumes that free will exists for mortals, and distinguishes that from creatures thought to lack free will, like demons and angels. Therefor, dnd is non-deterministic by default.)
The origin of this sapience, which was not the intent of their creators, is an open question.
Magipunk, and/or Gas Lamp Fantasy.
It is objectively not steampunk, bc it doesn’t use technology, much less steam and clockworks and Victorian sci-fi tech, and it isn’t a commentary on modern social and global politics through the lense of a subversive reimagining of the Victorian world.
In general, fantasy that plays with some of steampunk’s aesthetic, but doesn’t embrace tech or necessarily the subversive politics, is called Gas Lamp Fantasy.
But Eberron does embrace -punk politics in some ways, particularly some of those of Cyberpunk. Obviously it doesn’t focus on the looming specter of trans-humanism and the loss of humanity represented by it all that much, though that is a theme that exists in the world. What it instead plays with is the threat of international mega corporations and their ability to create super-national oligarchies that ignore the power of the State in order to better milk profit from the masses, the devastation of weapons of mass destruction, and the struggle to be recognized as a person by a world that only sees either a tool, or a monster, all while imagining a world that has DnD magic, and extrapolating what that would entail.
So, I like magipunk.