abirdcall
(she/her)
Really good point about the Barbarian having more specifics in the fluff. We refluff a lot at our table, and Barbarian is the class that gets the most fluff treatment. In fact, refluffed Barbarians are more common than the default, because of the issue you raised.
Treating fluff as mechanics that must be followed puts unnecessary constraints on the players. I totally agree there is nothing even remotely in the books that makes this a likely conclusion. I am sure the game designers are more than happy to see players put their own spin on the classes.
At what point do you disallow changing the fluff? Everyone has a line.
I disagree about the Barbarian having the most specifics, it might be true that people are the most lenient about changing the Barbarian fluff.
Would you be okay with a non-religious Cleric? How about someone taking Cleric and refluffing all the spells to be commands so they can play a 'Warlord'? Is that okay?
How about a Paladin without an oath? What about a character fluffed to be an Eldritch Knight but taking the Paladin class? If that is okay wouldn't it make more sense in the game to just change their casting ability to Intelligence and their smite from Radiant to Force? I think if you're okay with changing the rules of who the character is and what they represent, changing how that is expressed in mechanics goes hand in hand.
There are countless other examples. Somewhere we're going to find a line which a person won't allow. So how do we determine why that is and what guidelines can we use? What is our starting point?