money, power, connections,and privilege.
None of which are any use in the dungeon.
The3e Noble can get stuff for free because of their title. A noble would have access to connections and training that a street rat or sage would not. They can have access to the best schools, ship over the famous or exotic trainers, or have rare enhancements all before their start of their carreers.
Before the start of their careers. You have just described a 5e background.
If Lord Errond paid for an elf warrior to teach his children the longbow and his used his title to push his way not the secret areas of the Mage Circle's library, his son would know archery and arcana lore. If he uses these as an adventurer, he is using these skills he learned via his past status as a noble. And he'd shoot the demon with an arrow while shouting military commands after unsealing the cultist seal.
You have just described a 5e background. Meanwhile the noble does
not hone the skills of being a noble to a particularly strong degree while adventuring.
A noble would be doing the same. They'd be applying they skills they've learned in the dungeon
Unless they were planning a Red Wedding this is entirely different to the skills used at e.g. a formal banquet.
That depends ENTIRELY on the edition your're playing, since skills have been handled WILDLY different depending on editions. The skill system is handled radically different in various editions. There WAS no skill system in core 1e AD&D. . .with NWP's being added in some of the later books, and it was an optional rule in 2e (although, in my experience, very widely used) (or the "Secondary Skills" rule which was very bare-bones). However, there was a pretty broad skills system in 3e that was meant to encompass just about anything a character could do that didn't involve casting spells or using powers of some kind.
This is a thread largely about 5e.
Funny, in a lot of campaigns, to level up you have to take time off to train, and that can mean seeing a trainer. Is downtime for training not a thing in D&D anymore?
It's not really been a thing since 3.0.
That's like saying all non-nature-worshiping clergy shouldn't have the Cleric class. . .oh wait, they do.
Apples to oranges. Most nature worshipers are not clerics. There are for example druids, rangers, barbarians, and even people from classes without an explicit divine connection.
That's like saying most career criminals shouldn't have the Rogue class, but they do.
Not in any D&D edition I'm familiar with. In oD&D most career criminals are 0th level. In 3.X most career criminals are members of NPC classes. In 4e most career criminals are NPCs. In 5e most career criminals are NPCs.
Even if we are just looking at PCs then I question the statement that most career criminals are rogues. Given their lack of regard for either law or personal property there's a good case that most PCs are career criminals. There's certainly a case that most grifters and con artists are bards, and most thugs for hire are fighters and barbarians. A rogue is a highly specific archetype - high dex and sneak attack happy. Which is not how most career criminals work.
D&D classes are broad strokes. . .and from antiquity to only a century or so ago, from one side of the world to another, the same broad, general skill set has existed for aristocracy and gentry. . .of at least some combat training, with an emphasis on leadership, riding horses, academic learning above that of the common folk, and social graces.
So that's about two skills (history for the academics and persuasion for the leadership), riding, and some combat training. 100% of PCs have combat training - it differs from class to class what it is just as how different nobles approach combat are different. Two skills a background makes. And 5e does exactly that.
Specifics might change depending on society, but a 4th century Roman patrician, a 17th century Japanese courtier, and a 19th century British aristocrat would have much the same broad skill set, even if the specifics would change depending on the culture and weapons of the time.
Some academic knowledge, some knowledge of how to persuade and manipulate people, and some ability to ride. Yes they do have this in common
because that is literally what the background provides.
What they don't have in common is their fighting style, their relationship to magic, or the rest of things that they do as an adventurer.
but throughout history, and definitely in fantasy fiction, there's as much of a broad skill set and general archetype for a noble as there is for any other class in the game.
And in D&D 5e a background
does provide a broad skill set and feeds into the general archetype. A background provides literally everything you say they have in common.
What it does not provide is what they do when the rubber meets the road. A bard is a very good class for a noble - but plenty of fantasy nobles are flat out mages with the best tutors - and plenty of others are warriors with no spellcasting at all.
If you think even within the scope of Game of Thrones Sansa, Arya, Ned, Jaime, Cersei, Margaery, Khal Drogo, Jon, Daenarys, and Bran should all be the same class I'm going to call that ridiculous. But they have things in common, and that is what the background is for.