I wouldn't go that far. I mentioned Jedi and people got upset at the example. Yet you are saying there is no shared expectation. Everyone else in this thread seems to agree that there is a shared expectation that Jedi aren't a thing in D&D.
I think people also inherently know when they want something that is outside the rules. Now, many of them might assume that there would be no problem with it, but I think most people would still bring up their changes to the table.
And where is it written that the stuff some call 'hard rules' or 'mechanics' are not allowed to be changed?
People got upset because the Jedi, as you presented it, is such a far extreme to the discussion that it is nearly a parody of the discussion.
The issue being discussed is the idea that you class is an immutable aspect of character. To use an example featuring barbarians:
John brings a barbarian to the table named Ragnar. Ragnar's personality could be summed up thusly "Ragnar hate fancy talky man, Ragnar will kill talky man with bare hands, Ragnar not even wear stupid armor because Ragnar strong. Strong always kill weak."
To a different table, we have Fred bringing a barbarian named Clement the Third of Agnor. Clement is a knight of the realm, wears armor and carries a shield with his family crest. He is well spoken, educated (though more interested in matters of honor and battle than scholarly pursuit) and fights like a demon when combat is engaged.
Under the theory that "your class is your character", Clement is being played wrong. Barbarians are not supposed to be well-spoken characters who wear armor and care about honor. But, people point out, reflavoring the class to fit into this other mold is not difficult, and showcases the character they want better than making Clement a paladin or fighter.
Your Jedi example is more similiar to bringing up, "but what if the player wants to play Jerry Sienfield, stand up comic from New York City."
That has nothing to do with the actual discussion, it is a huge stretch to even see how it could apply to the idea of reflavoring a class or a concept to get the character the person wants.
Like the example earlier of the Rogue who was an ordained priest of a god. That is playing against type for both a holy man and a rogue, defying the expectations of the class and the concept, but it is a coherent character in the fiction who makes perfect sense.
That is the discussion, not whether or not this rule or that rule should be inviolable. Especially since some of the details are most definitely meant to be broken. Just flipping to the page on Elves I see "Most elves dwell in small forest villages hidden in the trees"
Except for the Forgotten Realms where they have kingdoms and massive cities.
Or Dark Sun where there are no forests, and elves are thieving sand dwellers.
Or Eberron where elves live on an island and worship their undead ancestors.
Heck, or two pages over where they talk about the Drow, who are elves, and live underground.
So, if even something as basic as "where do elves live" is mutable, why does my monk have to hail from a monastery? Why does my cleric have to be doe-eyed and naive about the world? Why does my rogue have to be greedy and know criminal elements?
There are details that can be changed, that can be seen from another perspective. If you want to say that playing a cleric who was a jaded drug user and smuggler who was granted a god's power when snowed in a humble monastery and conscripted to serve a god of justice is "changing the rules" then go ahead I guess, but you are putting rules where none exist.
