Some of the posters here are sorely mistaken about how Epic Spellcasting mitigation works. For example, backlash is dealt per round of a spell's duration and a given creature can only submit one spell slot to a ritual casting.
@OP: I'd suggest taking out all the most ludicrous shenanigans, like time-trait genesis planes. I'd also suggest removing NI nonsense and possibly all ritual casting. A time limit would be nice too.