Gods usually aren't pressed for quantum, and for the two gods that use growth creatures you're usually screwed anyway. And when you're not, mutate plus eat is just as good.
As to ablaze with Graviton, firestorm + eat is a much better move simply because it is permanent.
Eternity's main use is to keep yourself from decking, and with a large deck, you don't need to worry about that.
Granted, eternity is sometimes useful with rewinding your own creatures that are g-forced and such, but with large rainbows you usually don't have to worry about that. Also, pulverizer is useful against every god, and owl's eye is useful against most gods too.