Higher order: Gandalf or Balrog(s)

[pandora]

I think it is because the Istari were supposed to be uniting the people of middle earth, and not fighting their batle for them.

This is cart-before-the-horse thinking: the reason they were uniting people is because they were not powerful enough to overthrow Sauron themselves and their restricted use of magic and force was so that the uniting would be of the peoples' free wills and thus not an evil thing (as well as avoiding the damage it might cause). Otherwise the Valar are just playing a cynical game with the lives of the people of Middle-earth