Higher order: Gandalf or Balrog(s)

[Tuor Turambar,Cursed by the Valar]

Why not simply grab a Palantir and directly overthrow Sauron? A lot of people would not have had to die.

I think it is because the Istari were supposed to be uniting the people of middle earth, and not fighting their batle for them. Gandalf was not 'allowed' to look into the palantir and overthrow sauron, because that was not the reason the Istari were in Middle Earth in the first place.
If Gandalf had looked into the palantir, he would have been a 'rebel', lke Saruman.
Not to say he COULD have looked into the plantir, only that he WOULD not, even if he could.