To your first point. Griever is never shown to be anything scary to Squall, in fact he likes it. With all that Squall has been through, and his determination not to let his emotions get the better of him, why go to all that trouble for something would probably have recieved a blink from Squall, and nothing from anyone else?
To your second. That isn't evidence you referenced, it's the theory. Just as all other explanations for Griever are theories. R=U is just one of those theories, and it comes with the most evidence from the rest of the game.
