Disagreement is fine & good. Disagreeing with a front office decision is fine too. We’re unique as a fan base because there is a spectrum of Tom Brady to BB/system as regards to team success & everyone lines up on it differently. Judging by your username we both lean the same way to a majority Brady.
In the end that’s all we want is a good enough team around him. Rowe is a shaky CB2 & having two CB1s is a definite way to improve the defense. I just don’t know how someone like Nigel Bradham (overrated, look at the DL he has in front of him) & Preston Brown will help the LB group. Draft or bust there.
The defense is only as strong as its weakest link. The DL and LB units were the weakest links by far in 2017, largely due to injuries and FA losses leaving the Pats relying on several inexperienced players.
It seems to me, then, that the place to start "fixing" the defense is the DL - especially in the middle. Once an accomplished and
experienced player has been added to help with that, it affords the leeway to add a "lesser" (and less expensive), but
experienced, LB (Bradham, Brown, Casillas)
and a high-end draftee to improve the 2nd level.
After that, it may be prudent to add a high-end draftee to the safety group (where there's tons of experience), and a relatively cheap, but experienced player (e.g., Darby) to the CB group (where there's somewhat less experience than at safety).
Given the current state of the three levels of the Pats defense, paying a huge percentage of usable cap space to rent Sherman for a year would be like putting on a new roof to fix a leak while the foundation is crumbling and the walls are full of holes.