First comparison that came to mu mind was John Lynch. Lynch was a better tackler and better against the run than Williams. But BB released him due to his coverage issues even though he was a player he had tried to bring in previously and highly respected. I'm thinking that if BB couldn't find a roster spot for Lynch, then the chances of Roy Williams becoming a Pat are slim and none.
Lynch play has been off for a few years.. In his prime he was a great tackler but the short few weeks we saw him revealed that he no longer could meet the player head on..