True. But that secondary probably would have been a total disaster without him and Revis. Meanwhile, that DL was solid and the LBs were pretty good.
This season, the secondary won't be as good without Sherman, but it's unlikely to be a total disaster, either. Meanwhile, the DL and LBs need help to avoid continuing as the disasters they were in 2017.
If that Pats can scrape up $7M in cap space to pay Sherman, as glorious as that might make the secondary, I think it's smarter, and more beneficial to the defense overall, to invest that in the DL and/or LBs instead.