Actually was actually in a lower power position than the balrog in a way, despite both being Maia, because the Istari were sent to Middle-Earth in incarnate, mortal bodies, albeit long-lived, and could die.
True enough, but afaik Balrogs weren't really any more immortal. The forms the two take Id wager are more akin to different tiers of armor.
Gandalfs old man body might be the rusty iron the Balrogs demon-iron.