Re: The fix.
Platinum said:
With ANY prerequisite, it's still TOO powerful, because at epic level, the abuse potential is mind boggling.
The fix lies within the granted caster levels.
My fix is:
Only grant the +2 caster levels once every 5 levels and for the other levels, the class must choose which class's caster level improves.
IMO that's way too weak. You're drastically underestimating the importance of the lost caster levels.
If the player decides to split their caster levels evenly, at 16th level, they'll be casting spells as a 9th level cleric and a 9th level wizard. So a 16th level caster will only be able to cast 5th level spells tops, and not very many of those to boot. And they'll have a caster level of 9, which means penetrating SR will be almost impossible, dispelling will be almost impossible, and their spells can be dispelled with ease.
Utterly, utterly useless.
Or they could put all the levels in wizard, and end up as basically a 13th level wizard and a 5th level cleric... But are the spellcasting abilities of a 5th level cleric worth dropping from 16th to 13th level as a wizard? I don't think so.
I think the class as written is slightly overpowered, but not too much. It's only really a problem if the player goes Wiz7/Clr3/MT10. It's pretty well-balanced if the character takes even progression in both classes (i.e., Wiz5/Clr5/MT10). It might even be a little on the weak side at that point.
Oh, and I do agree with you that this class becomes very problematic at epic levels. If I were running an epic campaign, I probably wouldn't allow the class past level 10, even though the rules allow 10 level PrCs to continue advancing.