[The Might]

Giants existed, and that's more then clear.
In "The Hobbit", talking about Beorn's origin, Gandalf clearly says he heard him swear he would take revenge and return into the mountains, further speculationg he was perhaps a descendant of the olf bears living in that area before the giants came.
I doubt he means, before the avalanches or landslides or whatever started.
Also, Gandalf thinks about asking one of the nicer giants to help him and block the entrance to the tunnel leading to Goblin Town with a stone.
Clearly, they are not metaphores for anything.
They are however predecessors of the Ents in Tolkien's writings and this can be easily noticed by looking at this change from The Hobbit to LotR.

Selmo, as far as your post is concerned, I think I must disagree. I doubt the woses were trying to make a joke with that.
This description of Numenoreans as stone-eaters is clearly made out of awe, wonder and perhaps respect for the way they learned to use the stone to build their cities.