Fighter and Rogue are admittedly the hardest to differentiate considering they're the most varied, but take that sea of a thousand thugs, and you'll easily pick out the oathbreaker paladins, the evil clerics and warlocks, etc. And, again, that's assuming that they don't all have classes - we could easily be looking at a sea of fighters, barbarians, rogues, and the occasional other. We've already agreed that individual tables can vary how many people have classes, from everyone to PCs only. That makes your entire argument meaningless, because you're using different assumptions than others.
No, you won't easily pick them out, because NPCs have those abilities as well, and one that has that ability might not have any other ability from those classes and/or may have abilities from other classes as well. I mix and match abilities on the NPC side to get the result I want, and don't limit abilities to fit within class structures very often.
And my very point is that I am using a different assumption that others -- that setting, not rules is what allows the identification of class. You keep insisting that a rational observer could always pick out classes from the masses because they all share the same abilities, and I keep telling you that, with refluffing, those abilities don't have to resemble each other and that NPCs may not have the same set of abilities as classes (they can mix and match, or not have any, as needed). This would make it extremely difficult for your rational observer to pick out classes from the masses. Impossible, even.
The only way to solve this argument is if we come up with a baseline. Without a baseline, no one is arguing about the same thing. Its like trying to argue which is better for you - healthy foods, or therapy. The two are incomparable, since they both touch on very different things.
Yes, that is what people that want class to mean something in game want -- a baseline. I don't want a baseline, because I don't buy into the argument that class automatically means something in fiction. So telling my I have to establish a baseline so that you can pick out classes is anathema to my desires.
And I find this particularly amusing, because that's not my argument at all. In fact, my argument is "I object to the assessment someone cannot differentiate between classes without a PHB to reference in the default D&D setting." You are attempting to shoehorn me into a "side" when I'm not on either side. And I only spoke up against a specific flawed argument. It was unscientific, it made no sense. In a world where there are multiple instances of monks, barbarians, wizard, etc, you can compile and analyze abitlies and differences. And you will come up with the same division of classes.
And yet, if classes didn't objectively exist in game, you couldn't pick out the abilities and differences because everyone would do slightly different things across the whole range. This gets even more difficult if you add in multiclassing, which obfuscates clean class divisions even more.
When classed characters are the exception, rather than the norm, and when NPCs can have partial class suites of abilities, and when class abilities can be described as operating in many different ways (rage being the channeling of the gods' might, or a alcohol fueled anger-management issue, or a philosophy that involves welcoming death, or entering a fugue state where a rage demon possesses you), it gets really, really hard to do what you're suggesting is inevitable.
The only other argument I might have been making is that the default D&D setting uses the "everyone has classes and roles" baseline stance. And (related to that last one) it might include "it depends on the table, since homebrew settings are the most popular."
And you say you're not on a side.
I view the game mechanics as game mechanics. They exist to allow people to play a game. That game involves imagination to the extent that the imagination is supposed to overrule the game rules when it fits. So, to me, there are two things going on here, a cooperative fiction event, and a game. The fiction gives the reason to play the game, and the game allows a consistent interaction with the fiction. I don't think these need to be the same thing. To me, the game mechanics are an abstraction -- something that makes the interaction with the fiction workable; it boils down the interaction so that it is understandable and predictable (in the sense that you can predict your chances, not know them). So, yes, every character has a class, because that's the interface into the game fiction, along with the rules. But I don't see that the interface must exist in the game. Yes, the nature of the interface will affect how the game plays, but it need not necessarily affect the fiction.
So the class interface is already an abstraction to make interaction predictable. And when the world interacts with the players, it does so through that interface and the interface of the rules. But the interface is not the fiction, just as it's not the player. It's a handy set of tools and terms that allow consistent interaction. Let's say the player wants his character to use magic to blow up the bad guys in the game. The game provides the tool 'fireball' to do this, and sets preconditions for it's use. So long as the player's character has met these tool preconditions, he can then execute the tool on the fiction. The tool then interfaces with the game mechanic representations of the bad guys, does it's thing, and the players can determine the game outcomes. But, in the fiction, none of that has to occur. The character doesn't cast fireball, he calls to the elemental nature of fire, makes an offering to open the channel, and expends will to channel the result, and the bad guys blow up. No one has to think 'fireball' or 'third level spell' as those aren't fictional components, their interface components. Your fireball may look nothing like the next guy's fireball (yours is blue and whoompy, his is a giant orange face that speaks a horrid word before enlarging suddenly to engulf the area.
So I disagree that having roles and classes means that those things then exist, as a matter of course, in the game fiction.
At your table, you're right, and things work like you describe. At an Adventure League table, you'd be wrong (since the AL uses the default setting). Want to argue that the default setting (without any local interpretations, as strict to the official rules as possible) for 5e doesn't use classes for humanoids, I'd say that's one argument we could actually have. As things stand, however, no one is on the same page. Hells. I'm going to argue no one is on the same -book-.
Duh, of course I'd be wrong, because I wouldn't be representing that
setting properly. I have no issues with that at all. I'm not saying that there's a default or not, I'm saying that, with all of the fluff, you can choose to ignore it, change it, or go with it however you please in your games. In AL, there's the requirement that you use their setting and assumptions, and that's perfectly reasonable. I'd be upset if they didn't require it.