The thing that holds the work of JRRT apart from other "large" fictional constructs is the ratio of published canon to unpublished material. The inconsistencies between and among both actually ADD to the verisimilitude, I think: that's the way of myth. Disparate threads get woven together into a larger whole that looks different depending on the angle one approaches it from. The marvel of it is that all the threads came from the mind of one person, albeit one so steeped in so many myths that source material was hardly lacking.
And the underlying ubi sunt? or for JRRT, hwær cwom? is one of those threads, certainly. It was a strong current in medieval times, even early on, as the petty feudal lords looked back with longing to Rome and its perceived glory:
This masonry is wondrous; fates broke it
courtyard pavements were smashed; the work of giants is decaying.
Roofs are fallen, ruinous towers,
the frosty gate with frost on cement is ravaged,
chipped roofs are torn, fallen,
undermined by old age. The grasp of the earth possesses
the mighty builders, perished and fallen,
the hard grasp of earth, until a hundred generations
of people have departed. Often this wall,
lichen-grey and stained with red, experienced one reign after another,
remained standing under storms; the high wide gate has collapsed.
But for JRRT the words of another OE poem, The Wanderer
, may have come closer to home, given his loss of Smith and virtually all his other friends in WWI:
Sorg bið geniwad
þonne maga gemynd
swimmað oft on weg
Sorrow is renewed
when the mind surveys
the memory of kinsmen;
He greets them joyfully,
the companions of men;
they always swim away.