You are way over critical her Shmess. But in one sense you are right if VY had thrown the perfect pass like he did earlier, it would have been completed......just like every other pass ANY QB throws in the game. There IS no way a DB can defend a perfectly thrown pass.
However, after looking at the clip several times I think played it perfectly. I would contend that he was in man coverage on the WR and his proper technique would be to play the man from the underneath position with expected help over the top from the S. If you want to criticize someone, look at the S. I would say he was a bit late getting over there
BTW-what would YOU say would have been the correct position. If he stayed deeper than the WR, then he''d never be in position to cover ANY back shoulder fades, deep hooks, or in cuts, By playing the "under" position he's be in much better position to cover those 3 routes, and like I said before there should be S help over the top, but whoever the safety was on that play (I think Moore) didn't get deep enough in his drop and was a bit late breaking to the sideline.
BTW- in the long pass to Cooper early in the game. I've see replays and if you notice Arrington COULD have stayed deep the Cooper, but decided to be aggressive and by choice undercut him to take the inside position, and was beaten by the perfect pass. Anything less, and Arrington would have had a pick. If you get a chance to see a replay of that play I think you'll agree with me.