Gandalf vs Sauron?

[Andúril]

Captain Stern:
The only source I have is The Silmarillion and this is what it says in the 'Of the Enemies' chapter:

For of the Maiar many were drawn to his splendour in the days of his greatness, and remained in that allegiance down into his darkness; and others he corupted afterwards to his service with lies and treacherous gifts. Dreadful among these spirits were the Valaraukar, the scourges of fire that in Middle-earth were called the Balrogs, demons of terror.

So, it doesn't say that they Balrogs were "some of the most powerful" Maiar -- only that they were "dreadful"?

Come on! You must have something else -- oh wait, it looks like you don't...