The Balrog vs The Witch King

[Boromir88]

It is these times that I have called into question, not when WK met informants or Gandalf.~Raynor

But what this does show is that prior to the battle of Pelennor Fields the Witch-King was capable of using magic...so busting down a gate and lighting up a sword doesn't mean he suddenly had a boost of power. Why doesn't he use any of his sorcery when he encounters Frodo on Weathertop? I don't know, but he did us it when he encountered Gandalf on Weathertop. Or could it be that his task was different?

As I've said the Witch-King is hunting for the Ring, he's not out trying to kill anyone...not even the Ringbearer:

'They tried to pierce your heart with a Morgul-knife which remains in the wound. If they had succeeded, you would have become like they are, only weaker and under his command. You would have become a wraith under the dominion of the Dark Lord; and he would have tormented you for trying to keep his Ring; if any greater torment were possible than being robbed of it and seeing it on his hand.'~Many Meetings

Sending a jolt of fire from his eyes to fry Frodo wouldn't have been torment enough for Frodo. Sauron wanted this Ringbearer to suffer not have a quick and easy death.

That necessity was more than present previously and unlike Gandalf he had no restrictions.

But the quote above certainly makes it seem like Sauron limitted what the Witch-King was able to do. He wasn't trying to burn down the Shire or kill anyone who opposed him (he wasn't even supposed to kill the Ringbearer). He was to find out the location of the Ring and not only get the Ring, but also the Ringbearer, so the said Ringbearer could suffer.

At Pelennor Fields his is not limitted anymore. His objective isn't to bring people to Sauron to suffer...his objective is to completely trash Minas Tirith and kill all those who oppose him.

Gandalf indulged in far less impressive shows of power and yet he was still known as a wizard.

Aye, but Tolkien also refers to the Nazgul as sorcerers...and it is also the 'great wizard' Gandalf who calls the Witch-King a 'great sorcerer.'