So a Mystic Theurge needs at least 3rd level in each of a divine spellcaster and an arcane spellcaster, right?
I guess the main limitation of a Mystic Theurge is, now that Haste has been reduced in power, there's no more Hasted Quickened spells, so no more than two spells per round (and, having lost at least one and possibly two spell-levels of spell slots, they couldn't Quicken too high a spell, anyway).
Haste has been limited to no longer working on spellcasting, right?