First, I wouldn't call my approach RAW-based. Its actually based on the way people actually learn things, game balance, and the game's internal logic.
Your approach appears to match that of intent of d20 designers - that's why I called RAW-based approach.
Learning stuff is quite often non-linear, non-granular and non-deterministic.
Also, d20 is yet another incarnation of the system - internal game logic changes from one edition to another.
Second, I fail to see how the Simple/Complex/Exotic mechanic should influence my opinion on multiclassing.
Under a game system with all abilities working in the same manner (under AU, AE it applies only to magic classes - that's why my question was restricted to spellcaster multiclassing), switching from one class to another is not necessarily equal to gimping abilities from previous classes.
Its a mechanic very divorced from actual learning/practice; very artificial.
Let's not go there. I can quote you a ton of real life examples, where learning a single thing opened door to a whole world of new abilities (ok, just one example: programming).
AU/AE spellcasters learn entire classes of spells at once (as if they have a security passkey that opens all doors of a specific clearance level), whereas D&D spellcasters are learning specific spells (they have to acquire a distinct key for each and every door they can access).
Clerics.
Fighter and Martial Weapons proficiency.
Heavy Armors.
Linguistics.
This is RAW. The principle is the same, only the content is a little different (well, Clerics are not that different).
Also, you learn only Simple spells automatically. Complex and Exotic spells follow rules similar to Martial and Exotic Weapon Proficiencies.
[...]
Third (having looked over my AU but not my AE rulebooks, which are still out on loan) even in this system, Caster Level ≠ PC level. Your Caster Level = your levels in all casting classes (p71). IOW, a Magister5/Akashik15 casts as a 5th level caster. A Magister5/Mage Blade10 casts as a 15th level caster. Furthermore, that Mage Blade would only have access to Complex spells of 5th level.
Again, that's why I was asking about spellcaster multiclassing only.
Thank you for your reply.
Regards,
Ruemere