There are a couple of interesting thougths here but
JRR Tolkien already puts down many of these theories, he is a intentional enigma:
And even in a mythical Age there must be some enigmas, as there always are. Tom Bombadil is one (intentionally). Letter 144 JRR Tolkien
Two theories will break here first, He is
not a member of the Valar, nor is he more powerful than Sauron as Glorfindel states clearly here in
The Fellowship of the Ring:
"
But in any case, said Glorfindel, o send the Ring to him would only postpone the day of evil. He is far away. We could not now take it back to him, unguessed, unmarked by any spy. And even if we could, soon or late the Lord of the Rings would learn of its hiding place and would bend all his power towards it. Could that power be defied by Bombadil alone? I think not. I think that in the end, if all else is conquered, Bombadil will fall, Last as he was First; and then Night will come.
"I know little of Iarwain save the name, said Galdor; `but Glorfindel, I think, is right. Power to defy our Enemy is not in him, unless such power is in the earth itself. And yet we see that Sauron can torture and destroy the very hills" - Council of Elrond,
The Fellowship of the Ring,
JRR Tolkien
Note Sauron although incredibly powerful is still a Maiar; and a member of Valar would have no need to worrk about him. The difference between the two? Stated here in the Silmarillion:
"
With the Valar came other spirits whose being also began before the world, of the same order as the Valar, but of less degree. these are the maiar, the people of Valar, and there servants and helpers."
We also know that Tom clearly states he preceded The time of the Dark Lord:
"When the Elves passed westward, Tom was here already, before the seas were bent. He knew the dark under the stars when it was fearless - before the Dark Lord came from Outside." - In the House of Tom Bombadil
So he was here before Morgoth (than Melkor) who is said to be the first of the Valar to arrive on Arda here:
"Now swiftly as they fared, Melko was there before them..."
- The Coming of the Valar and the Building of Valinor ,The Book of Lost Tales
We can deduce that he is speaking about morgoth, when he says Dark Lord, not Sauron, due to the "
Dark Lord came from the outside" comment.
Tolkien explains further about Tom in Letter 144
" I would not, however, have left him (Tom) in, if he did not have some kind of function. I might put it this way. The story is cast in terms of a good side, and a bad side, beauty against ruthless ugliness, tyranny against kingship, moderated freedom with consent against compulsion that has long lost any object save mere power, and so on; but both sides in some degree, conservative or destructive, want a measure of control, but if you have, as it were taken 'a vow of poverty', renounced control, and take your delight in things for themselves without reference to yourself, watching, observing, and to some extent knowing, then the question of the rights and wrongs of power and control might become utterly meaningless to you, and the means of power quite valueless. It is a natural pacifist view, which always arises in the mind when there is a war" - Letter 144,
JRR Tolkien
Tom is just an intentional enigma, and by no means was he more powerful than Sauron.
Also most
Tolkien scholars, consider the Hargrove material largely Crackpot theories. He is not a maiar, his reaction to the ring makes that abundantly clear. he is not a member of the Valar as he states he arrived before Morgoth who was the first, and if he was Valar, Glorfindel would be much more confident in his abilities against Sauron IMHO, who was a Maiar.
We also no clearly he was not iluvatar himself who is God, by this:
"There is no embodiment of the Creator anywhere in this story or mythology" . Letter 181,
JRR Tolkien
Letter 181
Just some more food for thought, and discussion
I love
Tolkien's work
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