Oh? Can a Paladin fit in everyone? Can a warlock? Can a druid?
Seems like, if you require "uniqueness" to feel like there's an "identity" (and I wholeheartedly disagree/refuse to accept that premise), Fighter and Wizard "fitting in everyone" meets that criteria.
Just, going to remind you, we're talking about Class Identity in this topic. How distinct each class is
So, yeah, they can't fit in everywhere. But.... That's good? Like, that's specifically what the thread is asking? "Is this class specific enough it has its own tropes, own ideas, own stance". That's identity
Pretty sure a warlock or druid or sorcerer, for that matter, would disagree that using magic isn't a crucial part of (or even the base necessity for) their identity (whatever level/degree of identity that may be).
A warlock uses magic because they've cut a deal with someone else. A druid uses magic because they follow the old ways of nature. A sorcerer uses magic because they are born to wield magic, due to their history
They all use magic Because of something, not just using magic, and those elements build an identity to that class. How oother folks will feel about them, how their magic will be used, what other people doing similar magic may do.
So, irrelevant to this discussion of D&D classes, then?
How the wider market presents its classes in games is certainly relevant to talking about how D&D does it, even if we go beyond Pathfinder to "Its high point caused an actual visible blip on all TTRPG sales" giant World of Warcraft
So doing the damage, defending your companions, leading the charge (in many cases), giving as good as you get, taking more hits than others, and doing it all WITHOUT magical powers or invoked deities or loosing your mind with rage or mystical martial arts... Just your weapons of choice, your brawn (and possibly a bit of brain/tactics/"strategery"), your improving skill/experiences in battle....none of that "means something" as far as being a fighter?
That's not "unique" because other classes in the game engage in combat also?
I really don't have a response to this...that wouldn't get me in trouble, I think. So I'll just keep my thoughts here to myself.
I mean, that's one way you can build a fighter but, you said it up thread. Fighters aren't just that. So they aren't that identity because, they can be something completely different.
Y'see the problem? Fighters being the everyman robs them of an identity their own. And its absolutely easy to give them one, you've put it to paper, but then along comes "Well, we've gone and shoved this trope into the Fighter class now" and that identity is ruined again, due to it having to play as the holding bag for being generic. 5E ruins that identity you've given it by going "Well, here's the Arcane Archer, and its a Fighter now", completely destroying the defending your companions, leading the charge, and not using magical powers all in one fell swoop
Fighters and their subclasses should be recognisable as a Fighter, not "Huh that's basically my World of Warcraft hunter, thought that'd make more sense as a Ranger". You couldn't put a Marksman Hunter under World of Warcraft's Warrior, the closest equivilent to Fighter, but D&D basically lets it happen