Granted, Pio, and thanks for providing the quote, I still haven't read
Letters yet. I think, though, that certain of the feats of the Valar fall outside the realm of science as we now know it. Much like the Aboriginal legends of the dreamtime, or the appearance of the Hebrew god as pillars of smoke and of fire (although admittedly that could be metaphorical), and in fact many legends of previous times.
Failing to see a scientific explanation for events such as Eärendil's ascent to the heavens, or the creation and destruction of the Lamps of the Valar, I think that the Feats of the Valar must be either:
- outside the explanation of science, or
- described metaphorically by the recorder
I think the former is by far the more likely.
Also, re the migration of survivors out of Beleriand - didn't the Valar tow them to safety on an island? Or was that only the Númenóreans?