So, here we are in Day Whatever of my undefined mood. There is nothing good about it, but there are differences in how I think. For example, when I'm not particularly focused, I tend to think in the abstract/big picture sense. Case in point . . .
Being as how Mr. Gygax went to such lengths to stress that the LBBs were guidelines, isn't it possible that the classes given were: (1) Examples (2) Starting points (3) Some barebones to get things rolling? I know I have pontificated about using just the basic three classes. I was thinking about the Greyhawk supplement and the new classes in Strategic Review. It really occurred to me that the main three are starting points, they are the basic classes, the chassis, if you will. Look at all the variants and sub-classes of the fighter. It could be argued that they are attempts to power-up the fighter, but I don't buy that for two reasons: #1 - Why not just power-up the fighter? Why do you have to cook up a sub-type? #2 - The variants all have limits imposed upon them.
That bring me to another thought: How many referees out there stick to the book when it comes to limitations placed on classes? If a player wants to play a ranger, but his stat rolls don't quite measure up, do you fudge things in some way? I always did, mainly because players have always been in short supply and I didn't want to jeopardize the campaign before it even started by being inflexible during character generation. Now that I think about it, though, it's more than a little ridiculous. I'm from the time of Gygaxian Naturalism and my campaign design tends to bear that out. So, here I am trying to detail a consistent and internally logical world, but throwing consistency and logic out the window when it came time to roll up characters.
It is stated here and there in the books that certain classes are rare or uncommon. The rules support this notion mechanically by imposing restrictions on the classes. These restrictions make the class in question either more difficult for a character to take, and/or provide an undesirable counterpoint for the player to contend with. For example, the Paladin. This class requires a Charisma of 17 before it can even be taken. A 17 is a tall order, even if you roll 4d6, keep the best three and arrange to taste. Not to mention that the paladin is a fighter sub-class, so that 17 would be better served applied to Strength or Constitution. Then there's the fact that the paladin must be Lawful (we're talking Greyhawk here), and only associate with Neutral characters for brief, specific missions. If these restrictions are enforced, paladins would indeed be rare, because it would take a certain player and campaign to take the class.
Most of the classes outside the main three have such restrictions, that if ignored, can lead to them overshadowing the originals. I think that is the real strength of the original three classes; their versatility. If you do ignore the restrictions on the sub-classes and allow them to be more freely selectable it kind of wrecks the internal structure that supports the relative power balance between the classes.