Gandalf the white was never a member of the white council... It is uncertain who were the members but the council combined would defeat Sauron without the one ring if it was just the council members vs Sauron.
Think of it this way, we have one weaken Maiar against at least 2 Powerful elf Lords (Galadriel and Glorfindel), Glorfindel himself has already defeated a Maiar. The council also has three Maiar, Gandalf, Saurman and Radagast. The council might have also included Elrond and Cirdan but that is speculation.
The White council against Sauron with the Ring would be a more interesting battle, but he was still defeated by a Elf Lord (Gil-galad (who had not seen the lights of the two trees) and a man
Gandalf the grey was tired and operating under quite a few restrictions, "The Istari were forbidden to reveal themselves in forms of majesty, or to seek to rule the wills of Men or Elves by open display of power"
When Eru Intervenes and sends Gandalf back both his wisdom and power was much greater because he was refreshed and no longer a Istari sent by the valar but as a representative sent by Ilúvatar himself.
Agreed. Gandalf the White is brimming with power, anble to challenge the Nine, whereas Gandalf the Grey was sent packing when confronted by the same.
Gandalf arguably had the most power of the wizards sent to Middle Earth by Cirdan's own admission, but he had not realized it until the White Countil was no more.
As for this match, Sauron himself was more than a match for the White Council post-Mirkwood. Before that, he could be driven off, but not annihilated. It's debatable whether or not the White Council could challenge Sauron once he raised the black tower.