Before I deal with anything else, you guys probably need to set me straight on something. What is overpowered about the spellcasting? Seriously, what is overpowered about it? Apart from Rangers or Paladins, this was devised to be literally the least advantageous spellcasting system in existence.
By 20th level, you get 13 spells: 4 1st level, 2 2nd, 2 3rd, 2 4th, 2 5th, and 1 6th. All of them come from one spell list (or part of one for the arcanists). Each of those spells may be used only 1/day, you may not juggle daily uses between them, and can't ever switch them out. They are not used as SLAs but you get no bonus uses for high ability scores. You aren't even counted as using spell slots so I don't think the extra spell slot feat does anything for you. Metamagic, while arguable better than a prepared caster, is worse than a spontaneous caster as you have to sacrifice both a spell of the modified spell level and the spell itself (meaning that you can't sacrifice multiple spells to "get ahead"). The only nice things to be said is that your spells automatically restore each day and that you technically end up with more spells than the factotum.
Even though quickening spells as a class feature may look nice, it really only gives you 6 rounds of rather inflexible spellcasting before leaving you with a single 1st level spell. Similarly, casting 6 spells with metamagic feats would leave you similarly depleted. To reiterate, 13 spells per day/known at maximum.
At least, that was the intention. If people are calling the mechanics of the spellcasting overpowered, there is obviously something that I have missed or worded horribly that requires correction. Could you guys point out what it is?