”One can imagine the scene in which Gandalf, say, was placed in such a position. It would be a delicate balance. On one side the true allegiance of the Ring to Sauron; on the other superior strength because Sauron was not actually in possession, and perhaps also because he was weakened by long corruption and expenditure of will in dominating inferiors. If Gandalf proved the victor, the result would have been for Sauron the same as the destruction of the Ring; for him it would have been destroyed, taken from him for ever. But the Ring and all its works would have endured. It would have been the master in the end”
“Now the lightnings increased and slew men upon the hills, and in the fields, and in the streets of the city; and a fiery bolt smote the dome of the Temple and shore it asunder, and it was wreathed in flame. But the Temple itself was unshaken, and Sauron stood there upon the pinnacle and defied the lightning and was unharmed; and in that hour men called him a god and did all that he would.“
Honestly, he should just be "Unknown". The only reason for the tier is that the Maiar helped the Valar in the creation of the universe, but that's way too vague as it is. We don't know how much they helped or a timespan.
Not to mention that now that the "limited 4D" is gone, in order to get Low 2-C you need to be able to affect at least universal size.
And about the hypothetical Ring-Lord Gandalf, I'm not sure. Since even if Gandalf in base would be stronger than Sauron in base, that still wouldn't give him a flat out Low 2-C, because Sauron is High 3-A for the same reasons Gandalf is.
I don't think the "At least 6-B" is necessary. And I don't feel comfortable with the tier 2 rating. Personally I think they should be at just "Unknown".
Also about the Sauron tanking the lightning. Wasn't that done by the Eagles?
And out of the west there would come at times a great cloud in the evening, shaped as it were an eagle, with pinions spread to the north and the south; and slowly it would loom up, blotting out the sunset, and then uttermost night would fall upon Númenor. And some of the eagles bore lightning beneath their wings, and thunder echoed between sea and cloud.
Then men grew afraid. 'Behold the Eagles of the Lords of the West!' they cried. 'The Eagles of Manwë are come upon Númenor!' And they fell upon their faces.
Then some few would repent for a season, but others hardened their hearts, and they shook their fists at heaven, saying: 'The Lords of the West have plotted against us. They strike first. The next blow shall be ours!' These words the King himself spoke, but they were devised by Sauron.
Now the lightnings increased and slew men upon the hills, and in the fields, and in the streets of the city; and a fiery bolt smote the dome of the Temple and shore it asunder, and it was wreathed in flame. But the Temple itself was unshaken, and Sauron stood there upon the pinnacle and defied the lightning and was unharmed; and in that hour men called him a god and did all that he would. When therefore the last portent came they heeded it little. For the land shook under them, and a groaning as of thunder underground was mingled with the roaring of the sea, and smoke issued from the peak of the Meneltarma. But all the more did Ar-Pharazôn press on with his armament.