If one of our circlemates died, and we knew of a resurrection artefact, and couldn't craft one ourselves, we absolutely would storm the gates of hell for them. In fact, we have just recently stormed the gates of hell, and unleashed a weapon of mass destruction that is firmly in breach of "Thou Shalt Not Invade the Mind of Another" Law.
And, as I mentioned before, the "greek hero" is a load of sh*t attempt to devalue the good heroes did and do and their character.
1) No we wouldnt. Dead is dead.
We might move for someone who is only mostly dead, but whose soul has not passed on.
Someone who is dead is beyond our reach.
2)We stormed Yomi Wan for a living dude unjustly held.
We did so without mortal magic.
3)Greek hero is an explicit benchmark for the Exalted.
For every Perseus, there's a Jason.
They were mighty, not good, and equally capable of great good and great harm, often in the same person.
Arthur apparently wasn't dead though, I think. He was critically wounded and put to sleep. They needed the Cauldron to heal him, not to ressurect him.
I don't approve, but choosing to keep three heroes and a legendary prophesised saviour imprisoned in an afterlife is very on brand for a Yama Queen, so at least there's that.
The Cauldron of Rebirth raises the dead, it doesnt heal the critically wounded.
The QM might choose to riff on how things work here, but the versions of the Arthur mythos that the QM has referred us to appear to be the old Celtic stories as recorded in the Welsh Triads, not the Romances.
And in those, he died.
And in the end Arthur encountered the emperor, and Arthur slew him. And Arthur's best men were slain there. When Medrawd heard that Arthur's host was dispersed, he turned against Arthur, and the Saxons and the Picts and the Scots united with him to hold this Island against Arthur. And when Arthur heard that, he turned back with all that had survived of his army, and succeeded by violence in landing on this Island in opposition to Medrawd. And then there took place the Battle of Camlan between Arthur and Medrawd, and was himself wounded to death. And from that (wound) he died, and was buried in a hall on the Island of Afallach.
I don't believe that Jim Butcher's God practices moral relativism. King Arthur is a moral man by the Sword of Love's standards, i.e. God's standards, the same standards of very explicitly Christian virtue that Michael Carpenter holds himself to.
Arthur isn't a good person by 6th century warlord standards, but by the highest ideals of Christian moral thought. Which aren't so totally different to today, it's just that people didn't live up to them often, particularly rulers. King Arthur did though.
Jim Butcher's God is very much about grace, not worthiness.
You dont earn the right to bear a Sword. Dresden wasnt a particularly righteous person when Fidelacchius on his back levelled the playing field against Nicodemus.
Counterpoint:
Karrin Murphy.Who is a good person, but NOT a moral paragon of any sort, and yet wielded Fidelacchius at Chitchen Itza. Or Susan Rodriguez, who wielded Amoracchius at Chitchen Itza after more than a decade of wet work as a Fellowship assassin.
Or Harry Dresden, who most definitely isnt a moral paragon, but has been the guardian for not just one but two Swords.
I mean, Butcher has said George Washington was once a Knight.
George "Town-Destroyer" Washington. George "Owned 300+ Slaves" Washington.
And specifically for this quest, the myths we were referred to for reference are the Welsh Triads.
The ones where Arthur is pretty clearly a fairly conventional warlord.
So either the stories are conflating two different Arthurs, or you have it wrong for this AU.