[Boromir88]

Men who had gained a great deal of power from a dark lord.~Reader

This is what is said about the Nazgul after receiving the Rings:

Men proved easier to ensnare. Those who used the Nine Rings became mighty in their day, kings, sorcerers, and warriors of old. They obtained glory and great wealth, yet it turned to their undoing~Of the Rings of Power and the Third Age

But, the point obloquy is making, doesn't matter if they became "mightier," they were still Men, just 'greater' men. They still did not hold a lot of power over the fearless, and as has been shown Gandalf and the Eldar had sent them away several times, becuase they did not fear them.

You did notice the paragraph straight from the book where Gandalf, when asked if the Witch-King could match/defeat him, answered "It might be so," grimly and softly, right?

I'm assuming you are referring to this:

' Then, Mithrandir, you had a foe to match you,' said Denethor. 'For myself, I have long known who is the chief captain of the hosts of the Dark Tower. Is this all that you have returned to say? Or can it be that you have withdrawn because you are overmatched?'
Pippin trembled, fearing that Gandalf would be stung to sudden wrath but his fear was needless. "It might be so," Gandalf answered softly. "But our trial of strength is not yet come. And if words spoken of old be true not by the hand of a man shall he fall, and hidden from the Wise is the doom that awaits him. However that may be, the Captain of Despair does not press forward, yet. He rules rather according to the wisdom that you have just spoken, from the rear, driving his slaves in madness no before.
'Nay, I came rather to guard the hurt men that can yet be healed; for the Rammas is breached far and wide, and soon the host of Morgul will enter in at many points. And I came chiefly to say this. Soon there will be battle on the fields. A sortie must be made ready. Let it be of mounted men. In them lies our brief hope, for in one thing only is the enemy still poorly provided: he has few horsemen.~Minas Tirith

I explained this in my first post. We see Denethor's contempt for Gandalf..."Oh did you meet your match then?" I left out the middle paragraph because I felt like it held no importance.
1) 'grim' is not in there
2) softly counteracts what Pippin expected. Tolkien made every word count in his story and it's important to look at everything surrounding to get full meaning. The 'softly' is not Gandalf being 'grim' admitting he may be over-matched. It counteracts what Pippin had expected. Pippin expected Gandalf to blow up and get offended at Denethor's jab, but Gandalf keeps his cool and 'answers softly.'

He dismisses Denethor's statement, "you might be right, for the Wise don't know his end." But, notice the next paragraph Gandalf just flat out tells him no. "Nay," answering Denethor's question meaning..."No I have not met my match," he came back to look after the 'hurt men' and to tell Denethor to be prepared.

The Witch-King did not obey. He set his sword alight and was about to combat Gandalf when Rohan arrived.

The Witch-King left did he not? Therefor he did obey. Gandalf tells WK to go away. WK tries to play his fear card, laughing at him and doing some fancy tricks...but:

Gandalf did not move...~The Siege of Gondor

Gandalf did not falter, did not show any nerves, and the Witch-King goes away. IF the Witch-King felt like he could have defeated Gandalf he would have done so. As obloquy says Gandalf is the backbone of the alliance, 'he took command of Gondor's defenses,' as Denethor was just sitting back whining. If the WK thought he could be Gandalf, he would have done so. He tried to play his fear cards, it didn't work, and he left to Rohan's arrival.

Rohan's timely arrival may have been what fulfilled the prophecy. Note, first a prophecy does not have to come true, but Rohan's arrival makes the prophecy come true. Because had the WK gone toe-to-toe with Gandalf, the prophecy would not have been fulfilled, I'm sure about that.

If the fear was supernatural, and Eowyn was certainly not weak-willed at the moment, then that would mean that the supernatural fear was not fear, but a spell. Since a spell is magic and not fear, and the nazgul were said to gain power from fear, then the fear was not a spell, and the Witch-King did not use a spell.

This I'm just flat out confused...Eowyn did not fear death, but she certainly did fear the Witch-King, and would have been annhilated by him had Merry not stepped in:

Eowyn it was, and Dernhelm also. For into Merry's mind flashed the memory of the face that he saw at the riding from Dunharrow: the face of one that goes seeking death, having no hope...~Pelennor Fields

It's interesting, because we have Eowyn here, but Merry also sees a bit of Dernhelm's personality and is reminded of the 'face' when riding out to Gondor. Eowyn is not fearing death, but that doesn't mean she isn't fearing the Witch-King:

Out of the wreeck rose the Black Rider, tall and threatening, towering above her. With a cry of hatred that stung the very ears like venom he let fall his mace...~ibid

You should check out this post, where I talk about Tolkien's use of Boromir's height installing fear in Frodo. Same occurance is happening here, Tolkien is using the height of the Witch-King, over Eowyn 'tall and threatening' to install fear.

Sauron was one of the mightiest (perhaps the mightiest) of the Maiar.~Encyclopedia of Arda

While the EOA is one of the better sites, it still has it's flaws as it takes in what fans write and forms it's own the same. It remains that I have quotes from Tolkien's actual works to show that Sauron was called "greatest of Morgoth's servants." But, is never called "greatest of the Maiar." I think obloquy and I have shown at least 4 Maiar who were greater...Eonwe for sure, the other 3 mentioned it's not as definitive, but can be inferred, by their deeds.