Jester David
Hero
There's no shortage of character archetypes and roles that could be denoted as classes. Some broad and some small. Anything could be a class if you wanted.I would say that one of the major problems, however, is that when people list examples of warlord archetypes, they get dismissively handwaved away. "Oh, those are just fighters with leadership feats." or "Oh, those characters can't possibly contribute to our understanding of the warlord, since they commanded troops."
It's as if we were talking about rangers, and we were repeatedly met with "No, those aren't rangers. Those are just fighters with wilderness skills and feats." or "They can't be considered rangers, since they are mundane and D&D rangers must cast spells." If everything gets irreducibly reduced to being just a fighter with X, it's a miracle we have barbarians, rangers, and paladins at all.
My personal go-to is the jester. But there's also the black knight, detective/investigator, the gentleman adventurer, dragoon, samurai, ninja, corsair, bounty hunter, blood mage, shapechanger, etc. Some, like the death knight, exist in Warcraft and are thus incredibly well known and popular.
But just because something is a trope, an archetypal character, doesn't mean it needs to be a class.
The barbarian, paladin, and ranger totally do overlap with the fighter. As does the monk really. Ditto the sorcerer and warlock with the wizard. Really, you only need three classes: the warrior, the expert, and the spellcaster. Everything else is flavour.
But stuff like the cleric and ranger get included because tradition. They get grandfathered in because they've been a part of the game since 1st Edition. They've been included for two or three editions and a couple in a row. They're not just fantasy tropes, but D&D tropes.
Even then "person who leads people but isn't overtly magical" is a pretty weak archetype. Because it's so very, very easy to have a leader that's also a rogue or a wizard or paladin.