You're very fun to disagree with.
This actually isn't really related to QW;LFs, maybe very tangentially, but that's not the main point at all.
Never said it was. Just came to mind as I was typing. And I think it kind of stands, but whatever.
However, you're making a distinction that the D&D rogue is not bounded by semblance of reality in the same way as the D&D fighter.
Because Indiana Jones and spies.
What I mean is, when people look at the rogue class throughout D&D history, they point out fictional characters first. When people talk about fighters, examples often come from the real world, or characters we believe are real. Hercules might get mentioned, but no doubt he's mentioned after historical soldiers, war heroes, and all that.
You know for a fact that there are a lot of arguments on this very site where people get all up in arms about "non-realistic" fighters capable of feats similar to Hercules, who don't give a damn about an equivalent-level wizard's capacity to nuke a small city. That is what I'm getting at.
Rogues rarely - if ever - enter that discussion. On this site, we tend to give them more leeway. I blame Indiana Jones for this.
That's the distinction that I'm am disputing. I maintain they are both fundamentally "non-magical/mundane" classes compared to most of the magic-wielding D&D classes.
Why is this relevant?
I posed the question: Is there something UNIQUE about Fighters that mandates their sub-class design to being strictly mechanical?
And I think I've explained why I believe that situation is unique. I agree that rogues COULD exist in the real world, but I happen to believe that we seldom give them the same attachment to the real world that people give fighters. When we try to convert non-fighter people to the real world, we sometimes use rogues as the conversion class, and then say something like "well, obviously Cicero didn't have sneak attack....".
So then, if it's 3e we're using, we make liberal use of the aristocrat or expert classes.
If people accept your premise that fighters are UNIQUE, then it justifies the design decision to exclusively differentiate fighter sub-classes mechanically.
Fighters aren't unique. We DO sometimes treat the class as being unique, because we are much more able to make comparisons to the real-world with them. I just put forward a belief on why we treat them differently when it comes to subclasses . And that belief, if you'll recall, is that there are just so many examples of fighters that even trying to go down that rabbithole is a headache. I've seen pathfinder try it, and I personally didn't like it.
Keep the game broad, and you get better results. And the fighter is a great example of this, I believe.
If people refute your premise (i.e. that fighters are NOT UNIQUE just like rogues), then it calls into question the design decision to differentiate fighter sub-classes mechanically, whereas rogue sub-classes are differentiated both thematically and mechanically.
Sure! And you know what? I'm a bit unhappy with the rogue sub-classes for just that reason! I'd much rather have had an arcane rogue, and something like "acrobatic" rogue and "cunning" rogue, or who knows what. "Thief" and "Assassin" were far too flavourful for me. When I want to play rogue classes, I have to strip out the flavour and replace with my own.
Not a big problem, for sure, but one I wish wasn't there. I can't be the only guy out there who gets a bit squicky about playing an "assassin".
Also, you set up a false dichotomy. The only options (according to you) are super broad fighter sub-classes or a vast multitude of fighter sub-classes to cater to every possibility.
Those are the two big ones, yes. In my opinion, of course. At it's most basic level, do you want Pathfinder, or do you want BECMI? I choose the latter. I've done the former, and I'm tired of going through the SRDs to find a class option I can pick from to replace that Shield Slam ability I get at level X, because the character I want to build doesn't use a shield, and if I don't replace that power, I'll be underpowered and the other fighter in the group will outperform me.
Blech.
I'm sure there are different options. You can add a few subclasses. I've already said this upthread. But I'd vastly prefer general subclasses that can be flavoured multiple ways as opposed to specific flavours (like the rogue's assassin) that suggest a specific mindset and character type. That sort of thinking is much more imaginative to me than having the designers being creative and expecting you to just shut up and play. So, to reiterate, "mounted warrior" instead of "knight". "War Leader" instead of "Centurion". And so on.
It's been a while since I've had a good bollocksing! And to that, I say, "Flim Flam!"
It's about sufficient coverage. Wizard with 8 sub-classes provides sufficient coverage for the various types of wizards. Why would you think the same couldn't be done with a fighter?
Well, it COULD be done with the fighter. I have no doubt that it could be. I'd just prefer they strip the flavour away. As for the wizard, I think the 8 subclasses was a design decision they got locked into. Either they move away from the established "specialists" of older editions, or they include all 8 specialists. They could've just done three or so, but you KNOW there would have been nerd rage over that. So they covered all 8 to keep some happy fans.
I doubt they had the page count to do 8 subclasses for each class, though, so they tried to keep things brief when able.
That's just a theory.
As an aside, my litmus test for classes in any game (and subclasses in 5e) goes like this: If I had a group of 5 players, and two players played the same class, would those players overlap in character? Even if their characters had similar mechanics, would they seem to be pigeonholed into similar personality types, or gameplay decisions?
None of the subclasses in 5e have that problem, I think, with the exception of the Necromancer and possibly the Wild Mage. I'd compare that to Earthdawn, where the character disciplines are so tight (and yet so specific, unlike BECMI) that it would seem like one swordmaster would be pretty similar to every other swordmaster.
I bring this up because ultimately, I don't think the number of subclasses really matter. They only really exist to give fun options and variations on a play experience. But all D&D classes (in all editions!) are ultimately broad enough that they don't much overlap in actual play.