- Fighting-Man, Magic-User
- Cleric, Illusionist
- Ranger, Druid, Assassin, Monk, Paladin, Bard
It seems obvious to me that the Fighting-Man and Magic-User classes together represent one approach to classes, while the Ranger, Druid, Assassin, Monk, Paladin and Bard represent an entirely opposed approach to classes, the same approach followed by pretty much all classes created for D&D in Dragon Magazine, Unearthed Arcana, later editions or supplements, or even old school renaissance publications.
The Ranger, Druid, Assassin, Monk, Paladin and Bard are quite definitely professions. They are what a character does for a living, and their abilities -- and they have a lot of abilities -- are designed to help them perform in their profession.
In contrast, the Fighting-Man and Magic-User resemble professions, but are really ways of approaching problems: archetypes. The Fighting-Man solves problems physically, usually by hitting them. The Magic-User solves problems magically. They actually have very few abilities: the Fighting-Man can use a greater variety of weapons and armor, progresses faster in combat ability, and can fight off multiple 1 HD creatures; the Magic-User can learn, prepare, and cast spells.
We can argue about where Clerics, Thieves, and Illusionists fit between these two extremes. The Cleric in theory solves problems through faith in some other being, represented by the turn undead ability and to a lesser extent by the way cleric spells work, but has fighting and magic abilities that are a little too strong. The Thief in theory could be an archetype rather than a profession, but instead of solving problems through craft and guile, Thieves have much more focused abilities plus an alignment restriction imposed because they are conceived as a profession. Illusionists could have been handled as Magic-Users with a unique spell list, but they wind up with a unique experience progression and special item restrictions, making them feel more like a profession.
What I wish had been done is that the game had stuck to the archetypes end of the spectrum and instead added very simple guidelines for modding classes. For example, instead of a separate Illusionist class, keep the Illusionist spell list as an option for Magic-Users, perhaps with a minimum Dex requirement and an experience penalty for the privilege of access. Clerics and Thieves might still fit as separate classes, but I think they need to be seriously redesigned.