I have found definitive proof that Dark Souls top tiers are universal tier if not higher. Nito was said to have introduced and personally oversees the death of all living things, and literally Nito is like a low or mid top tier in Dark Souls, not even one of the strongest beings.
I was skimming through your thread and some questions popped up in my mind.
1. How strong do you believe Shiryu and Magellan have been pre- ts?
2. Do you think it's possible that Shiryu has been on par or even stronger than Yami Teach? (he even commented on leaving, if Teach would have failed gathering Wb's df https://i.imgur.com/0WXQGG2.png
3. How strong do you believe current Shiryu is?