istari rank

Here's a poser for you. The Simarilion describes Olorin as the wisest of the Maiar, and certainly when you consider what happens to the other Istari by the end of the Third Age -- two Maiar lost without a trace, Radagast off playing with animals and generally uninvolved in the affairs of the intelligent races, and Saruman corrupt -- Gandalf clearly does the best job at following Eru's purpose.

That being so, why was Saruman made the head of the order, and why does Gandalf generally defer to him?

I suppose one could argue that Saruman's desire to lead the White Council was a portent of how the passage of time eventually would lead him astray into seeking temporal power as well, but then that leads me to wonder where Curunir was standing in relationship to Melkor when Eru led them in the symphony that created the universe.

A scenario that involves Curinir jockeying for power because he desires it, and Olorin being content to let someone else have it, seems to match their personalities by the end of the Third Age, but one wonders what they would have been like at the start of the age, when Eru had just sent them into the world.