I've only read about half the thread but wanted to get some thoughts down before I forget.
Personally, I prefer to provide organizations over class structures in game. For example, if I were to have a group of mage cops in a setting, it would be made up of many different types of people. I see no reason why a monk or rogue couldn't be a member of such an organization, as they could no doubt contribute significantly, even if the organization has a disproportionate number of artificers. Moreover, it seems odd to me that this organization exists, but no other major groups of artificers (such as an Alchemists Guild, or even something more secretive like something based on a group like the Masons).
That's assuming that class is a thing in the game world itself, which isn't my preference. In my games, a class is mostly just a useful grouping of abilities for the purposes of character creation. If a cleric introduces himself as such, people will understand that he is a man of faith, but there are other folks in the world who call themselves clerics without the benefit of being able to wield magic, or even so much as a mace. Similarly, most people in the world use the terms wizard, warlock, and sorcerer interchangeably. Only those learned in matters arcane comprehend the distinction in such terms.
In my opinion, even in a world where class is a reality, any sufficiently large organization to have significant recognition would typically rely on more than just one class. Sure, you might have a dozen wizards who are part of the Wizards Only Club. But even if the founders of the aristocracy were all sorcerers, at least some of their descendants probably either didn't inherit the magic, or simply decided their interests lay elsewhere. Just because someone has a talent doesn't necessarily mean they will nurture it (my little sister is a gifted artist but chose to pursue a PHD in Microbiology instead).
All that's to say is that I agree that giving characters hooks with which to tie them to the setting is excellent. However, I don't agree with giving it strong class connections. An added benefit of disconnecting these organizations from class concept is that players now have a larger variety of organizations to choose from.
To address your first Unique Point: The Alchemist's guild isn't -exclusively- Artificers. But Artificers, which are a rare group of people whose profession largely sprang up in recent years in a single town, are the most well known members because of their unusual method of handling things. Like I said, in a different thread about the Ashen Lands, their original purpose was keeping the sewers of Falconhurst clean and functional, so anyone with skills in:
1) Alchemy
2) Chemistry
3) Investigation
4) Architectural Engineering
5) Fighting criminals, misfits, or monsters in the sewers
Is more than welcome to join. But the class fantasy of Artificers for the setting is tied up in the Alchemist's Guild. That's also why it isn't called "The Artificer's Guild" when that would be more reasonable for an Artificer-Only group.
To address your second Unique Point: Not all Nobles or even Royalty are actually Sorcerers. But sorcery runs in Royal Families (and many old Noble families) due to the power initially bred into the bloodline by the various sources. And any Sorcerer who -is- a Sorcerer and -is- a Royal can always go Prince Harry, marry Megan Markle, and move out to pursue his own lifestyle away from the Royal Family... but everyone sill knows he's Prince Flippin' Henry wherever he goes.
Again, the point isn't to shoehorn every character into a neatly constructed box and keep them there, it's just to give players a sense of place in the setting for their character's skills, talents, and origin in the world's narrative, so that they and the NPCs have a shared understanding... Which of course can be directly undermined or manipulated for gain on one side or the other.
You're fixated on names.
My point is if Alice the Archer, Sir Bob the Knight, Wicked Charles the Gang Enforcer, Danny the Dandy Duelist, Captain Edwin of the Red Kraken, Freddy the Farmer's Boy from Westfield, Sargeant George of the Town Guard, Scout Hixal of the Elven Vanguard, Duchess Isabella of Eastford, Purple Jack the Psi Warrior, Eldritch Sword Kassandra, and. Lumos Guminson of Clan Urgrand are all fighters then the image of a fighter is muddled. The assumptions of fighters become few. And the usefulness of the term is weakened.
The who point of a class having a meaning is that the members have some big unique noticeable they share and/or a lot of small similarities.if fighters share nothing, it's only use is to display mechanics.
At this point you're more discussing a matter of Design Philosophy than a matter of cultural narrative, Minigiant. And your philosophical problem is based on nomenclature. I.E. the naming of things.
I get it. You'd rather have 1 whole class devoted to each of those roles. Maybe 2-3 classes which can more "Closely" split focus between those roles.
By all means, feel free. But that has never been the topic of this thread. Fighters, for all of their variety, are directly supported by pretty much every setting's narrative. And generally in a manner which encompasses many, albeit not -all- of their subclasses.