Let's actually examine this from the opposite direction. Would you allow a 3rd level Commoner in the party, if he could also cast Charm Person, Charm Monster, Disintegrate, Fear, Finger of Death, Flesh to Stone, Inflict Moderate Wounds, Sleep, Slow, and Telekinesis at will, in addition to being able to make a 150-foot Antimagic Cone just by looking in that general direction? And let's not forget to mention that our Super-Commoner is also able to fly, permanently.

Now add in that our Super-Commoner can also do three of these things in any given round, in addition to having access to the most powerful prestige class in the game.

It's not reasonable on any level, is what I'm getting at.