There is a nasty habit among reductionists to gut anything flavorful out of a class and reduce it nothing more than a means of delivering X ability.
Actually, I think there is a nasty habit of class-centric thinking to unnecessarily marry anything flavorful to a class, creating unnecessary constraints on what abilities can be mixed so that one style (the Okinawan Peasant-Monk) gets supported but boggart's design space so another style can't exist (the Chinese weapon-monk).
By reductionist logic: a wizard and a sorcerer are two separate classes as they do two different mechanical things, but the paladin and fighter should be condensed into a theme/background combo, despite the fact that "fighter" and "paladin" are not overly similar concepts while "sorcerer" and "wizard" are practically synonymous.
Actually, the Wizard and the Sorcerer have the same power source and the same ability niche (Arcane Magic). The Paladin, however, is a hybrid of both the Fighter and the Cleric's niche's (martial prowess, divine power). Essentially the Wizard and Sorcerer are just Magic-User sub-systems, while the Paladin actually pitches his admittedly small tent in the territory between two Cardinal Classes.
This is just 4e all over again. "Replace "class" with "role" (Defender, Leader, Striker, Controller), and "theme" with "build".
Nope. Between Vancian Spell lists and Themes it seems pretty clear that you can explore "roles" with themes like "Defender" or spell selections.
It would be closer to the mark to replace "class" with "power source, combat aptitudes, and hit dice" and "sub-class" would relate to specializations - like a combat style for a martial character (great weapons, bows, martial-arts, rages), or a spell allocation system for a caster (Vancian, Book of 9 Swords, Power Points, Prepared vs. Spontaneous, etc.).
"Build" would be a more rounded character archetype involving theme and background - the monastic mystical martial artist; the barbaric raging reaver; the harrowed magician who steals power from devils; the privileged, high-born knight, etc.
The point isn't the eliminate what made up the Monk class, but to liberate it.
Again, why stop there. Why can't a magician be a Holy-man?
Arbitrary distinction between Divine and Arcane magic.
Why can't a Warrior be a Rogue?
Arbitrary distinction between Finesse and Force attacks.
They could be eliminated, but those tropes are considered Core to the brand identity.
Take the 4e monk and tell me what it has in common with the 4e fighter.
Role? Nope. Power source? Nope. Weapons and armor? Nope. HP? Nope. Powers? Nope.
Role? Striker. The Essentials Fighter is the Slayer - a striker just like the Monk.
Power Source? The 4E Monk was a psionic. Psionics weren't even Core from OD&D to 3.5E. That's completely alien to every previous incarnation of the monk, and 5E so far doesn't have anything Psionic in its Core.
Take the 3e monk and tell me what it has in common with the 3e fighter.
BAB? Nope. Saves? Nope. Special abilities? Nope. Alignment? Nope. Speed? Nope. Skills? Nope. HD? Nope.
Let's not romanticize things, though. The 3E Monk was a train-wreck of a class with tons of design flaws at its core.
BAB? Both the Fighter and Monk needed optimal BAB. Only the Fighter got it. The Monk flailed around with Flurry as a poor substitute.
Special Abilities? Both shared an overlap of Bonus Feats, only the Fighter got everything the Monk got and more. Other special abilities the Monk had overlapped with the Barbarian, Rogue, and Ranger.
Alignment? The Fighter definitely benefited by not be type-cast into an alignment restriction.
Weapons? The Fighter could use the Monk's weapons, and weapons that the Monk was prohibited from using due to being Japan-centric instead of more broadly inclusive to Chinese-inspired Monks.
Between alignment restriction, bad BAB, M.A.D., and straight-jacketed "special ability" progression that Monk was a terrible multi-class candidate in an edition that measured optimization by multi-classing or caster levels. To cap it off, one of the few good multi-classing options for the Monk was a 2-level dip into Fighter for the HD, BAB, and Bonus Feats he should've already had because pretty much all the depth in martial-arts style fighting was found in Fighter Bonus Feats. The only thing keeping the Fighter from obsoleting the Monk entirely as a Martial-Artist was the expanding Unarmed Damage Die mechanic and the pile of suck you got if you tried to Power Attack with fist instead of a great sword.
Both can be described as "classes that hit things in melee until they fall down?" Bingo!
Actually, they can both be described as "classes that fight in melee with options for a bunch of special maneuvers via Feats that now fall under 5E's 'Combat Superiority' mechanics."
The big problem with being hyper-classist like AD&D and 3E were with their Monks is that you basically roll up a bunch of thematic material that could be more broadly applied and marry it to a combat style, then basically feel compelled to keep them away from other applications to keep up the idea it's a unique and precious snow-flake of a class. Then other builds get eliminated because they overlap too much with the Okinawa Monk without fitting his mold (like the Chinese fighting monk, the Zen-archer, the non-combatant monk, and the non-monastic martial-artist).
- Marty Lund