If you or anyone else takes the time to make a list of all the plays that (fill in the blank) did not perform to whatever standard you hold, it stands to reason that is all you will see. However it makes that list useless since there is no equal comparison with his peers.
No different than someone looking to make a positive result, right?
Yes, that would be absolutely correct. That is precisely why I suggested that if you planned on reviewing those games again that you attempt to do so with an open mind, rather than simply looking for reasons to validate your already formed opinion.
As games were unfolding live last season I often had the same initial reaction as you. I would re-watch those games the following week; last night I re-watched several once again, fast forwarding in order to only review the defensive snaps.
My conclusion is that the biggest deficiency in the Pats defense overall and the pass defense in particular was the play of the safeties. Far too often the corners were left alone to twist in the wind without enough support from James Ihedigbo, Sergio Brown or Josh Barrett. Their subpar performances too often left the cornerbacks in unwinnable situations.
To me the second thing that stood out was not enough pressure on the opposing quarterback. On an alarming percentage of pass plays the Pats got little or no pressure on the opposing QB; far too often he seemed to have all the time needed to make a throw, and with open passing lanes as well.
The third thing that I noticed was Devin McCourty. He seemed to have trouble knocking a receiver off his route in press coverage, and also seemed to have trouble knowing when to turn around to pick up the pass after chasing down that receiver that went by him.
While the group as a whole was certainly nothing to write home about, after re-watching several games (I'm planning on watching the rest this weekend) Arrington was not only not the worst CB on the team, he looked to me to be the best. I suppose I could make the case that Ras-I Dowling was the best CB on the team, but does it really make sense to rank a player that played less than one game as 'the best'? To me the answer is no, though others may disagree. Based on what I have reviewed so far I would rank the 2011 Pats corners as being Arrington, McCourty, Moore, Bodden, Molden, Phillip Adams, and withhold a ranking for Dowling.
Perhaps you are right and I am wrong, but from what I watched Arrington outperformed at least five (if not six) other Patriots at cornerback in 2011. At the bare minimum he was not the worst corner on the roster last year.