I disagree with the 3 easy, 3 medium, 3 hard thing.
You want variety. Some weeks they may be nigh unfarmable, but some weeks they would be all ferox, paradox, destiny, neptune, and miracle. That's what makes the idea so appealing to me
.
Furthermore,
the point is to make you able to make a good deck that encompasses them all. It isn't to keep the current farming statistics.
The idea is to make it so that if you can make good decks, then you can farm FGs easier since you can make a deck that can easily beat 5 or so out of the 6-8 FGs (I'm starting to lean towards eight).
In line with this idea, I would almost suggest that the FGs for the week for YOU is random and isn't the same as the others. So it's not like a single good deck builder can just go post a deck that wins against the week's false god's; instead, you have to figure one out yourself.
Can YOU think of a deck that can consistently beat eternal phoenix, seism, paradox, hermes, graviton, rainbow, and ferox? If you can, then you deserve to be able to farm FGs for those 3 days or week or however long it lasts.
Also, Zanz could then "streamline" the easy FGs so that they're a large amount harder, since you would have a smaller pool of 6-8 FGs to choose from.