Dear Mbo, Second rule of literary criticism is: "Don't believe everything an author tells you" (first rule: "Beleive everything an author tells you"). It is only not an allegory in the strict Dantean sense: a one to one matching of narrative to alternative meaning structure.
As I said, and did indicate that it was a matter perhaps of taste, the last book might be better if it was physically at the end of the world, by which I meant physically back in the pseudo-England of the shires -- a bit like England in 1940 -- in the last ditch. I suspect Tolkien was afraid that the allegory with Dunkirk would be too obvious, and switched it around. Because of the dynamic of the narrative -- the good guys move into the territory of the bad, their last ditch is forward ground -- it never feels to me as if the armies of good are on the brink physically. I appreciate you think this is heresy, and am always willing to be corrected by an immersed fan.
More heretical: I think the Lord of the Rings is fun, but not very influential as literary work -- because the linguistic form of the material is not as powerful as Tolkien's superstructure. He did not create a new epic language to match his epic, as say Milton or Spenser did, in spite of all his scholarly nestbuilding. He tried, and should be congratulated on the effort, but almost nobody in this century has figured out how to write a modern epic in new cast epical language that will work: Joyce and Pound maybe.

I think what people will read in 2100 will be The Hobbit, as a minor children's classic, and of course his original scholarly work on the Old English and Middle English classics. Not a bad legacy.
yours, Peter T.