AuraSeer said:
Sure it will, because he doesn't use those slots for attack spells. He buffs his entire party with bull's strength, remove fear, protection from elements, death ward, spell resistance, hero's feast, and every other beneficial cleric spell he can think of. That's effectively free, because it doesn't use up any of his arcane slots. All his wizard spells are still available for for offensive use.
So a Mystic Theurge offers more buffs than a Wizard or Cleric. Is that necessarily overpowered, or is it necessarily a bad thing? No. Buffs have their limits. They can be dispelled. They have time limits. They're a limited resource. They take time to prepare and use.
The usefulness of buffs will vary from game to game, from party to party, from situation to situation, from fight to fight. How often does the party have time to buff up before a fight? That's a question that's almost completely in the power of the DM. How often does the party know in advance what they're facing, and what spells they _really_ should have used to protect themselves against the enemy? Again, the DM has considerable control over the situation.
More buffs can be more fun for the game. A party that's short on buffs will likely see those going to the Fighter, because that's smart strategy. Except that means the Ranger and the Rogue get to suck even more now, compared to the Fighter. Now everyone gets a buff. Is that necessarily so bad?
People who hate the Theurge argue that it hardly pays any cost in offensive power. I disagree, there is a considerable cost, in terms of highest level spell that can be cast, number of high level spells, save DC, ability to penetrate SR, and other potential losses from not taking another PrC.
The theurge has a little less combat power than the wizard does, but far greater flexibility. It would be weaker for a one-on-one arena situation, but IMO it appears potentially unbalancing for an actual campaign.
Yes, it is potentially unbalancing for some campaigns. I'd say the same about several spellcaster PrCs. But a DM who understands the limitations of the character, and takes those into consideration, will probably (IMHO) not have a problem with the Theurge. The Theurge may be overpowered, but it's certainly not broken.