[devilsgrin]

Though i am not in anyway saying that Gandalf is weaker than the witch-king, but the witch-king did break gandalf's staff during their minor confrontation in Minas Tirith... and as their staves are the symbols of the power of the itarii one could conclude, that originally a man or not, the Witch King is undoubtedly one of the most powerful beings in Middle Earth.

Though to say that Gandalf was the most powerful being in Arda would possibly an exaggeration. Many of the first eldar are still alive, and their power would be considerable. Tolkein saying so doesn't make it canon, as papa tolkein was occasionally contradictory and often changed the meanings of things in later letters, etc...
For Gandalf the Grey to have fallen to Saruman proves that in the least Saruman the White was his then equal - though clearly more cunning by far.
Sauron without the ring may have been weak, but he would certainly have been more powerful than Gandalf. Gandalf against the Balrog did include a ring as well recall. the word Minion is key also... rarely are minions more powerful than their masters unless they are grossly stupid... and the Balrog being a demon from the earliest days of arda is unlikely to be stupid.

Bombadil was master of his domain, tho i wonder what that power would be outside of it.


As to other potential council members i would most certainly include Celeborn, Glorfindel would be there naturally... he is reputed to be the most powerful elf in Rivendell... aside from Elrond with his ring, and he was quite a figure in the wars with Angmar especially.
Thranduil seems likely as well. Erestor would possibly have had a seat due to his association with Elrond and Cirdan, and of course his reputation as highly wise. Gildor ... who knows... we really only see him as little more than a warrior... but given his age its likely he would have had his own share of knowledge and wisdom to contribute.
I'd also agree that the current chieftain of the Dunedain would be there aswell...as aside from elven scouts, the dunedain seem to be chief agents of the council's will.