One one hand it makes sense for there to be only 8 survivors,
Why? There were a lot of coneheads in that ship.
but on the other it beggars belief that the Gliders (and presumably the Sun Folk and the Wave Dancers) were all descended from only 3 elves. Any thoughts?
For that reason alone, I'd say it's myth. Or maybe those eight elves started the Wolfriders. Maybe different groups started the sunfolk and the gliders. Maybe Rayek heard the story from Pike or Skywise, and therefore thought it might be myth.