It goes like this:
[3-A] Golden Master Sword >>>>>>>> True Master Sword [At least High 4-C] > [At least 5-A, likely High 4-C] Master Sword >>>>> [At least 6-A+] Weakened Master Sword > [At least 6-A+] Goddess Longsword > [6-A+] Goddess White Sword [2 Petatons from Faron's feat]
Basically Faron and Base Ghirahim are now just stronger than the mini-bosses [not Twinrova], but inferior to the later dungeon bosses that are fought with a Link with a Master Sword.
At least 6-A+: Morpha, Bongo Bongo, Phantom Ganon, Volvagia,
High 6-A: Twinrova, Botched Ganon, Oracle and Awakening Link, Wind Fish Nightmare, Wind Fish, Breath of the Wild Link, Ganon's Blights, Possible the Guardian, Malladus, Spirit Tracks Link,
I think 2 petatons is 6-A+ since is above the mid of 760 Teratons and 4.435 Petatons, close to High 6-A, which would make sense with Bellum and Malladus statements.