Quinn said:
I wouldn't mind hearing your reasoning about why the PrC is balanced a bit more. I don't think you'd be hiring Sean Reynolds or Monte Cook based on their answers. 
I wouldn't necessarily base my hiring on the final answer, but more based on how they frame that answer. Both SKR and Monte have addressed concerns that are important and point out their mastery of the system.
There's a few things that make me look at the MT as a balanced option. One of them is based on the raw, number-crunching aspect of game design. This is the part that most people see as important. That's true, but it's only half the equation. The other half is player expectation. Most of the time, this factor is embedded in the first one, but sometimes it can leap out and clobber the math and balance behind the game.
One of the important parts of balancing anything is what I see as the "What do you do now?" factor. Basically, a character can only do one thing each round. If you take two characters, face them off against each other, and one character has better options over the course of the typical D&D encounter (6 or so rounds) then that character is more powerful. This is where the MT has big problems. Sure, he has lots and lots of spells, but at any given moment a spellcaster who stuck to one class has a better, more useful spell available. In the typical party of four (fighter, rogue, cleric, wizard) the mystic theurge doesn't displace anyone. At any level, his best spell comes up short. What he can do is provide lots of buff spells for the rest of the party. But, since he is terrible in combat (d4 hp, worst BAB progression) once he uses those spells he doesn't have much left to offer. Generally, it's best to have the cleric burn spells to improve the party and let the wizard keep his magic for combat, since the cleric can always wade into combat with his mace. The MT does shine in the middle to late portions of an adventure, when the other casters have gone through spells, but at that point he still doesn't have the firepower available to overpower anyone. The raw number of spells is nice, but the offset in SR-defeating ability makes up for that. Over any given encounter, a wizard is going to outgun the MT against similar monsters.
The second half of the equation, and IMO the more important one in this case, is the issue of history. In 1e and 2e, multiclassed spellcasters were a viable option. The odd thing with 3e is that these classes have suddenly become much less useful. One of the issues I have with the multiclass rules is that not all class levels are created equal, yet they are treated equally under the rules. The first level of ranger or barbarian is more valuable than the first level of wizard. This causes problems with a lot of multiclass archetypes, many of which have their root in 1e and 2e. Since veteran players expect these options to be open (and heck, they're fun to play) it makes sense to support them.
History is a powerful force in game design. You can't simply take a viable character type that's been around since the late 70s and drop it from the game. I think prestige classes are the best way to get around the issue of multiclass restrictions, since they solve the problem of not all class choices being equal at higher levels. Personally, I'd like to see more prestige classes like this, ones with little flavor but a distinct, mechanical focus that makes multiclass characters more viable.
