Interestingly, it did refer to the same review by Edwin Muir that you identified. The following passage is on pg. 148.
"Edwin Muir's complaint was that the whole work was sub adult in its painlessness. 'The good boys, having fought a deadly battle, emerge at the end of it triumphant and happy, as boys would naturally expect to do.' There is a simple reply to this, which is to say that Frodo does not end up well or happy, and that he avoids any suggestion of triumph, seeming in the end incurably scarred, a 'burnt out case.' He is admittedly taken away to be cured of his wounds, like King Arthur... But there are other people, and creatures and things, which cannot be taken away or healed. In fact, it is much easier to make out a case for Tolkien being a pessimist than as a foolish or childish optomist; it is another of the qualities that mark him out from most of those who have imitated him.
Thus, it is obvious that many of the senior characters in the Lord of the Rings envisage defeat as a long term prospect. Galadriel says 'Through the ages of the world, we have fought the long defeat.' ... The whole history of Middle Earth seems to show that good is attained only at vast expense while evil recuperates almost at will... Morever, it is made extremely clear that even the destruction of the ring and the overthrow of Sauron will conform to the general pattern of fruitlessness...The destruction of the ring, says Galadriel, will mean that her ring and Gandalf's and Elrond's will all lose their power, so that Lothlorien 'fades' and the elves dwindle. Along with them will go the Ents and the dwarves, indeed the whole of Middle Earth, to be replaced be modernity and the dominion of men."
The passage then goes on to suggest that Tolkien placed his characters in such seeming hopless circumstances in order to give them opportunity to show courage against evil and rise above. He therefore removed "easy hope from them."
Does anyone know where in the South Miami area LOTR is being shown with the preview?