The reason I proposed equalling was to limit the effectiveness of the spell. If they are equal, then the chance of getting hit is 50/50. However, the other way would be to make them the second-weakest, with a limitation in the number of rounds. Testing might be the bst way to determine which is more balanced. Also, I added the principle above (transposition).
"Mentor's Watch" Makes the weakest creature in a ritual look as strong as the second weakest creature. This should prevent the weakest one from constantly getting killed, which is important when you're trying to level it. If this is overpowered, then limit it to lasting 3-5 rounds. Edit: This would be for the Transposition principle (as you are switching weaknesses).