[Zigûr]

The whole point of the Wizards was to give counsel to the inhabitants of Middle-earth and guide them towards victory, not to lead them against Sauron. The Wizards were not "generals." Saruman tried to make himself one when he should have been turning his efforts towards aiding Men and Elves. Gandalf ended up having to do the duty of at least three Wizards on his own. Perhaps in different circumstances they might have managed a more organised defence against Sauron. Besides, when the Wizards were sent, Sauron's military strength was not nearly as great as it was at the end of the Third Age, insofar as he could be considered to have military strength at all rather than manipulating various factions on diverse campaigns. Similarly I don't think the impossibility of destroying the Ring was well-understood. Why would Gandalf have bothered with the attack on the Morannon otherwise? Hoping for a miracle, perhaps. That was the belief of which Saruman had become incapable. But as a rule I don't think that, prior to its identification, the Ring actually figured especially substantially in the policies of the Wise towards Sauron in any event. They believed, perhaps erroneously in the end, that some form of victory was possible. I would argue that if the essential role of the Ring had been understood earlier things would have been different. Elrond and Círdan might have been more insistent with Isildur, perhaps.

Saruman betrayed his mission and betrayed the Valar. He refused numerous offers of redemption. He was incapable of admitting that he was wrong and that his faithlessness was ultimately revealed to be unjustified. What place was there for him in the West after that? Would he have even wanted to return if permitted?

I would argue, perhaps, that Sauron played the Valar very well indeed over the course of the Second and Third Ages, forcing them into an apparent stalemate such that their efforts probably did seem hopeless. He had reckoned, however, without Eru.