HAHA! You're playin' my JAM! Organizing classes? Are you kididng me...clear your calendar. I can do this for DAYS!
<I hear the moans and groans, now. "Oh gods, Steeldragons talking about classes again. I know, people. I know. It's a sickness.>
Let's start here. Most of you have probably seen this [periodically] over the last few years:
SO, beginning there...you see my generally preferred mode of breaking all classes into four cardinal points.The traditional "Big 4" of the games origins, used explicitly up through 2e, and kinda left "unspoken" since. I tend toward referring to them, collectively, as: the Warriors, the Wizards, the Priests, and the Rogues.
Originally the Fighting Man, Magic-user, Cleric, and Thief and their alterations of title from edition to edition. The broadest archetypes you can have. If you can play a knight, or a gladiator or a barbarian or a scout or, or, or, you can make it a Fighter and just do the rest through equipment and roleplay. Do you want to be a witch, a sorcerer, a "Gandalph/Dumbledore" kind of wizard, a Merlin or Circe kind of "wizard," or, or, or, you can make it a Wizard[Mage] and just do the rest through roleplay and some re-skinning/flavoring/backstory. And so on.
The categories are boiled down into their most concentrated distillations: What are Warriors/do they do that other classes don't or can't? Warriors are dependent on and defined by their Combat Skill/Styles.
Wizards are dependent on and defined by their use of Magic that is harnessed/directed/mastered by the Self (either literally or access to some all-pervasive universal source/energy, such as FR's "Weave," that would be available to anyone). Whether these are Arcane energies or Natural or Elemental or Primal or however else you want to collect the type of magic/spells, the caster (his/her knowledge, his/her ancestry, his/her force of will, happenstance, etc...) is the source of their own magic-use.
Of late, I have replaced "Priests" with "Mystics" to allow for that servant of a greater "other" power, but not necessarily a deity/divine origin and not necessarily a member of a religious order. But the general category and how it interacts/combines with the other cardnial points still holds.
Priests/Mystics are dependent on and defined by their use of Magic & Combat ability, embodied in the first default option of this caster/non-caster combo of the Cleric. They are further differentiated by the source of their Magic being something OTHER than that personal imbued/learned/figured out or mastery of some all-pervasive radiation, but something "outside" or "beyond" the individual. Yes, even the traditional [shaolin stlye] "monk" who is a master of their own enlightenment are, really, reaching beyond/outside themselves to greater heights of spirituality/divinity and the powers that come from there. Hence, the Monk -or a Mystically-flavored variant thereof- also counts as a Mystic class.
Rogues fairly self-evidently are dependent on and defined by their use of Skills, predominantly non-Combat related skills, though some combat ability is not entirely out of place (hence "Assassins" and "Avengers" being considered Rogue classes). Rogues rely on what they know how to do more than how they handle themselves in a fight.
From there, the next "tier" of classes are those direct combinations: the Fighter+Cleric = Paladin; the Mage+Thief = Warlock (perhaps) or to my mind, Illusionist (the magic of deception); etc...
From those 50/50 classes, the rest become shades of grey...how about the guy with more "fightery" but still divinely inspired or empowered, what about the guy who's more "cleric-y" than fightery? What about the class that combined Divine and Arcane magic leaning toward/with a splash of rogue skills. So things -depending on the game- like amounts of "non-weapon skills," "backgrounds," "archetypes," etc... those sorts of third or fourth layer of traits and features further shade different types of characters...and whether those shadings are distinct enough to warrant themselves as their own full class (or existence as a subclass of another full class) becomes more and more delicate and subjective.
SO, there's that. The classes are essentially branching trees from the 4 cardinal points of Non-Magic: Combat skills/Magic: From Self/Magic: From Other/Non-magic: Non-combat Skills. Who's a Warrior/Wizard/Mystic/Rogue/? The more of one "base" tier class or the other decides where in the hierarchy the classes go. Tradition and longevity within the game/across editions is another factor of where and how close to the base a class becomes.
With every new "tier" we need to have abilities more and more specialized and, I would submit more Ability Score dependent, either/or with a minimum Score, a need for multiple minimum scores, or both.
So the base game would appear to have something like this:
WARRIORS
Fighter - guy who hits reliably, damages reliably, stands longer than most, NO magic guys, Fighting Styles
--Knight/Cavalier: guy who hits the most, special thing "Virtuous Styles" (Cha. based)
--Barbarian: guy who damages the most, special thing "Rage Styles" (Con. based)
--Martial Adept: guy who stands the longest (mostly due to good saves, movement, damage reduction and deflection features), special thing "Disciplined Styles" (Dex. based)
Paladin - guy who hits reliably, damage reliably, stands longer than most, adds divine magic & auras, Oaths
--Vanguard: guy who hits best and gets the most magic, special thing "Defender's Oath" (Wis. based)
--Warlord: guy who saves best and gets the most auras, special thing "Leader's Oath" (Cha. based)
--Blackguard: guy who damages best, special thing "Foresworn Oath/Banes" (Con. based)
ROGUES
Thief - guy who uses skills the best, move reliably, hits/damages reliably. NO magic. Tricks.
--Acrobat: guy who moves the best, special thing "Tumbling Tricks" (Str. based)
--Assassin: guy who damages the most, special thing "Killing Tricks" (Con. based)
--Swashbuckler: guy who hits the most, special thing "Panache Tricks" (Cha. based)
Ranger - guy who uses outdoor/wilderness skills best, moves reliably, hits/damages reliably, adds a smattering of magic, Trances.
--Avenger: guy who hit the most, gets a little divine magic, special thing "Divine Trances" (Wis. based)
--Warden: guy who damages the most, gets a little nature magic, special thing "Nature Trances" (Con. based)
--Investigator: guy who gets the most auras, gets a little arcane magic, special thing "Deductive[divinations] Trances" (Int. based)
I have a game to get to...but you get the gist...I'll go into the other half dozen ways we can categorize things later tonight or tomorrow.

Bate that breath. BATE IT!