Each Istari had a different mission?

[Legate of Amon Lanc]

Originally Posted by Rhod the Red

Saruman may not have gone bad if he wasn't
grovelled so much by M-e leaders. If, for example,
(forget his name) the Steward that gave him the
key to Orthanc never did that or allowed him
access to the Minas Tirith archives, lack of access to
the Palantir & a fixed abode may have mitigated,
if not prevented, his evolution of thought.

I don't entirely agree. I agree that probably getting Orthanc further inflated his ego and gave him the excuse to lock himself up and start building his own little empire (not to mention the temptation of using the Palantír, eventually), but it certainly wasn't the only thing. Certainly you can't say Saruman did not have it "in him" to be the authoritative type. I am not sure if I recall correctly, but I think he asked for the keys of Orthanc in the first place. And in any case, you can see already in the Unfinished Tales, in the description of the Council, that he had this desire to be the "First" with everything that comes with it (he was jealous of Olórin already there, that much the text implies).

And lack of access to the archives - that is ridiculous. Saruman (or in fact, all the Istari) was supposed to help the folks of Middle-Earth, among other things, with their knowledge. A Steward should then come and say "hey, you have no permission to look into my archives"? That'd be pretty stupid, wouldn't it? Denying information to your allies sounds quite nonsensical to me. After all, it's only information - but what one decides to do with it, that is what counts. And as we know, Saruman eventually used e.g. some of the knowledge of Sauron's to (possibly) for example breed Uruk-hai... but that came from his own mind.

And as for Radagast, see above. Remember that he failed. Radagast was on the opposite end of the spectrum from Saruman, but they were both extreme. Radagast went so far in his, as you say, "humble life in the wild" that he got totally out of touch with the "real" world around him, out of touch with the Free Peoples and their problems. (Saruman had the opposite problem, he had forgotten that nature is something more than just tool for the humans. But they both made a critical mistake.)