Sub-systems in OD&D

I had a thought today during my run.

OD&D has about 4 subsystems.
- D20, roll high. Used for melee and missile combat and saving throws. Important to all characters to some degree, except perhaps for mid-and-high level MUs and high level clerics.
- 2d6, roll high. Used for Turn Undead and for reaction/morale checks. Of most importance to Clerics, but also important for fighters with entourages.
- Vancian Magic. Binary fire & forget consumables. The earliest forms of magic didn't even have saving throws, so this is at heart a non-chance mechanic.
- D6. Used for misc checks (dare I say, "skill checks?") like Secret Doors, Opening Doors, etc.

Progression through the game

One interesting thing about this set up is that it requires low level players to really only know two sub-systems.
Fighting Men: Needs to understand the D20 very well, and maybe 2d6 for morale.
Magic-Users: Needs to understand the D20 somewhat and a little bit about Vancian magic (only has one spell per day, remember?)
Clerics: Needs to understand the D20 pretty well and the 2d6 for Turn Undead (level 1 clerics didn't get a spell in the Old Days)
Dwarves: Needs to understand the D20 like a Fighter as well as the single D6 for "skill" checks.
Elves: The most complex of the classes; needs to have a handle on D20, Vance, and the D6.

At higher levels, the Magic-User (and to a lesser degree, the Cleric) don't care about the D20 to hit roll at all. They have so many spells at their disposal that they have switched over almost entirely to Vance and their odds of hitting have fallen off so dramatically that it isn't even really worthwhile rolling a D20. This is cool because it creates a qualitative change through the game experience. Magic is earned. And with the right to wield magic comes the chance to use a new mechanical sub-system.

You see the same thing with other old school materials. Druids get shape-change at mid-levels. Assassins get thief skills at level 3. Paladins and Rangers get Skills at low levels and Vancian magic at high levels.

This progression makes me wonder if I'm doing the right thing with my hack in giving each "class" its own clearly differentiated mechanic right from the get go. Perhaps its better to start everyone on a core mechanic and reserve use of the more complicated or involved mechanics (like Vancian spells) for the mid to higher levels. That is (A) easier for new players by providing a learning curve and (B) creates a reward and feeling of progression as levels are gained and qualitative changes occur.