Zhure said:
The only thing the multiclassed caster loses out on is higher level spells, but he gains a breadth of lower level spells.
I wish people would stop putting forward this argument. It is the height of sloppy thinking. Only higher level spells? Hardly.
One of the most important rolls in D&D Magic is the saving throw. The high-level spells have a couple of important factors:
* A higher DC, because it's based off spell-level
* Many don't have saving throws at all.
A good example is
maze a top-flight 8th-level spell. No save, no spell resistance (at least in the 3E version). You might well say that the 5th level spell equivalent is
hold monster, which has a Will save and Spell Resistance.
Ah... there is a problem.
When you add to that the fact that many low-level spells are capped for damage, then they really don't stack up.
Fireball does 10d6 damage for a 20th level caster under your system. The 20th level caster is using
meteor swarm, dealing about twice as much damage.
In a combat, your 20th level caster takes more than twice as long to deal damage as my 20th level single-class - if damage is dealt at all.
Now, there must be some trade-off for the versatility of the cleric/wizard, but the gap in power between a 10th level wizard (even with caster level 20) and a 20th level wizard is extremely significant - and is more significant than the versatility.
The one other factor to consider when creating such a system is that it is simple and easily applied. The system you've described
is simple, but still leaves the multi-class spellcaster as far inferior to his single-classed brethren.
Yes, a multi-class should be inferior, but for what can be a fun archetype to play, I think that much is a problem.
Cheers!