[HerenIstarion]

Welcome to the Downs, Kaszul [img]smilies/smile.gif[/img]

There are two points in your post I deem incorrect:
1 Gandalf is not gaining power in the duel with Balrog - he dies first (in fact, them both do), and then is returned into the world again, by whom - remains unclear, either Valar or Eru himself. Even in this case he is not more powerful than he was, but he's got more wisdom and authority, and is allowed to reveal more of his original power than he was before.

2 Gandalf was not trying to get the world rid of balrog. Two reasons are there - first of them given by Gandalf himself - he says he's too weary already to fight such an enemy, Another one is that Balrog was inside Moria for quite a long time, showing no inclination to come out. It's possible that Sauron would like to draw such a powerful spirit to his side, but it's not shown anywhere in JRRT's works, so assumption must be made that Balrog was going to stay inside Moria after Gandlaf's death as well (if it was victorious, of course).

+ if you judge by modern standards, the offended side was Balrog, not Gandalf and Co, for they broke into his private property and were trespassing [img]smilies/rolleyes.gif[/img] . Poor, poor Balrog. [img]smilies/biggrin.gif[/img]