The gods are saying "they can't interfere with the mortal world", but they already interfered when they banished a god to that realm. If you are going to stripe a person of their power and banish them, you should strip them down to the same level as the creatures living in that world. Not to "just a bit weaker than a normal god" level.
It's like taking a lion and putting it in a cage with a bunch of sheep. Sheep start disappearing one day and you figure it was the lion. What do you do to rectify the situation? Get three Rams from a different farmer to protect the sheep. Sure the Rams might be able to beat the lion with some luck, but you can't tell me that you didn't have the foresight to see the complications that could arise. You are gods for cripes sake.