Aren’t Neanderthals much shorter than humans?

They were, but also stronger, IIRC.

I figured "giant" could be a metaphor, after all it's in a collection of traditions of pastoralists, wherein God rejects the agriculturalist's offering, who then kills his sheep herding brother.

Then the farmer builds the first city, and his descendents are the first blacksmith, the first musician, the first dancer (debateably), and the first animal farmer - who also often conflicted with semi-nomadic herders.

Great metaphor for the Iron Age equivalent of the Range Wars.

Could Neanderthals be described as "heroes of old, men of renown"?

In my head canon, some Neanderthal managed to find acceptance in Homo sapiens societies through prodigious feats of strength or bravery.

IIRC, Neanderthal were far stronger than us.

Mind you, could be that they're where folk memory of dwarves arises, short, strong, like living underground.

Maybe elves were Homo floriensis?

I love speculating like this because it's entirely unprovable, much like evolutionary psychology.