Mattachine
Adventurer
This discussion is even more of a mental exercise than most on this board. Having the fighter is a certainty in the new edition.
The problem is that even if the fighter is all of these he's still the most useless class in the game because he can't DO anything besides hit stuff with a hunk of metal. He can't move obstacles out of the way, he can't talk his way around a fancy dress party, he can't stop a demon from carrying a princess back through a hellish portal.
Giving the fighter more plus signs isn't the answer. He needs effect buttons, he needs something on his character sheet that allows him to tell the DM "now this happens" instead of begging for the DM to come up with rules for him to swing from chandeliers on the spot.
By your stretch to include bards and druids we might as well call everything that can hit stuff a fighter.
Thing is, the fighter can be those dozen classes you want to replace it with. Those dozen classes however, cannot do anything other than what they're doing. That and the fighter is as much a staple of the fantasy genre as the wizard is.
Why not look at all the editions instead of just 4e? Every edition has had Fighters (or a very close equivalent) and has yet to suffer for it.And you have confirmed that you tend to defend 4E before thinking.
We are talking about this in the face of a new edition, a edition which will be defined by its core rules and not dozens of splatbooks which are required in 4E to broaden the scope of the fighter.
Just looking at the core rules of 4E the scope of each class was very limited. Does 5E continue this focus? If yes then fighter does indeed need a little overhaul to define its role better.
After thinking about it for a while, if there's anything Wizards needs to do with classes is reduce them. The OP is right that there's a whole bunch of niche classes out there, not just for the fighter, but for every class. What's worse is that these are often so specific, that no other class gets any of the features, leading to the ridiculous level of multiclassing attempts to get a more thematic or power-build that read something like:
Fighter 1/Ranger 2/Rogue 2/Barbarian 1/Druid 4/Cleric 2/Wizard 7.
What Wizards ought to do is reduce the number of unique classes and have all the niche classes become "builds" for specific existing classes.
A Barbarian is essentially a Fighter that rages. A Ranger is a Fighter that uses bows. A Sorcerer is a Wizard who doesn't prepare their spells. A Shaman is a druid variant. Why do these need to be unique classes? All it does is lead to class bloat, spell bloat(repeated spells for different classes), feat bloat(similar feats that do the same thing but only for different classes), ect...
Why not simply have The Fighter; which you could build a Barbarian, a Ranger, a knight(non-divine caster). It would get rid of the ridiculous need for multi-classing if you could simply jump around within a general class framework of "My main purpose is to hit things!"
Instead of killing off the fighter or any of the "big 4", why not kill off all of the specialized, niche character classes that have cropped up over the years?
Doesn't solve the problem...
because what is the fighter than doesn't rage, doesn't live on the edge of civilization, doesn't follow a knightly code, or isn't a military tactician?
What is a fighter that is just a warrior? And how do we make him an unique type of adventurer?
By allowing him to be a cosmopolitan fighter.
So why don't we just have the fighter be that instead of trying to cram all of a previous class into a new class feature?