Gandalf vs. Sauron (Hobbit Movie Spoilers)

[TheLostPilgrim]

In the latest Hobbit film, we see something utterly ridiculous, something that never happened--and would never happen--in the books: A duel between Gandalf and Sauron. And Gandalf, despite holding his own briefly, is quickly trounced and imprisoned. It is a cheap magic battle straight out of Harry Potter or Dungeons & Dragons.

While again, this would never happen in the books...IF it did happen, if Gandalf and Sauron had indeed fought, I have some questions:

1) If Gandalf was put into a situation where he was face to face with Sauron, would it have been permitted by Eru/The Valar, for him to uncloak himself and use the full might of his power, as we got an inkling of in his battle with the Balrog? Would that have been an acceptable time for him to "lift the veil" of Gandalf and allow the power of Olorin to be in full might?

2) Could Gandalf "uncloaked" have defeated Sauron?

I ask since, technically speaking, Gandalf and Sauron are kin; Both Maiar, and thus both of the same kind and (theoretically) strength. Gandalf was one of the people of Manwe, who is equal in strength to Morgoth, whom Sauron served--This too would seem as evidence that Gandalf and Sauron were "on equal footing" so to speak.