Because I think it definitely fits the wordings of the various Prophecies and the plot development we saw (e.g. Rand's interactions with Alivia) better. On the other hand, I have no reason to believe that Gawyn will suddenly become crucial in Rand's plotline. I also don't see why Rand's girls would have to bring Rand's corpse to Tar Valon on a boat (besides that the particular Prophecy states that Rand on the boat is dead but alive then). In my view, Rand will simply come to the realisation that he has to fake his death to trick the Shadow, also using the dull dagger, while Logain will seemingly take his place.

As said, the fake death-theory (or at least the idea that it only appears to the world as if the hero died, while he is actually still alive) is also based on myths or other fantasy/science fiction series from which RJ borrowed, like the Greek myths or Dune. IIRC, also the earlier versions of the King Arthur myth said that Arthur was just badly wounded, but actually survived and didn't die. There are also critics of the Bible who argue that Jesus actually didn't die on the cross, but just fell unconscious and was later revived. Rand's "death" could be an example of changing of myths, namely that he actually didn't die, but this resurrection will be the future story.