Cazorla didn't hide. He backed himself to be able to use his skill to compete with bigger players. Vieira hides, and I don't think its out of cowardice but out of pragmatism. He doesn't have the strength of ability to retain the ball in the face of your average PL mid or defender applying pressure. If you can't do that you can't play in this team, its what the whole thing is built upon.
If he doesn't get stronger we'll never find out if he's good enough.