I think the fact that Williams has only had one complete season in his career is even more of a knock against him, and as you mentioned, he was even injured in the one year where he did play all 16 games. A player certainly cannot do much about injuries, but it doesn't bode well for the detractors who could add "injury prone" to the list of reasons to hate Roy.
Injuries and missed games aside, I know what Roy can be. I still remember the game against the Lions where he was completely unstoppable and made our defense look like the London Silly Nannies. That's the Roy I am holding out for.
Like I said in my other post, it just comes down to confidence for both him and Romo. Roy needs to forget about trying to prove anything and just go out and play. When he doesn't live up to his own set goal of proving everyone wrong, he just gets more down on himself. You can see it in his expressions and his defensive stance every time he is interviewed. In this league, talent alone is not enough. A player needs confidence like a fish needs water. If he focuses less on the media and what everyone thinks and more on playing football the way that his natural ability will allow him to do, he can build that confidence and the rest will take care of itself.