Here's my theory I posted in a different thread (just an educated guess)

"I really hope it's 1:1. Honestly, even with that ratio, you still can't buy that many Myth pieces. If you have 2,000 Philos (which I do), and you end up getting 2,000 Myth in exchange, that's really only one chest piece and one leg piece with 350 left over - not even enough for an accessory (and that's for one job)."