Look, the Patriots have 12 picks in the 2020 draft. That's plenty to find good players to fill out a roster loaded with veterans with lots of post-season hardware. Forget the second round pick.
Sanu only had a $3.7M cap hit in 2019 and a $6.5M cap hit in 2020. This was a good move at the time given the injury to Henry, the issues with both Josh Gordon and Antonio Brown.
Belichick tried to pull every rabbit out of the hat he could find knowing that Brady wasn't signed past 2019. Mohamed Sanu is a good player. With a training camp, a clear role, and time with Josh and the other WRs in the room, he'll be fine this year. A core group of Harry, Meyers, Edelman, and Sanu is a good place to build on. Belichick will add a WR and pass catching TE in the next couple of weeks.
The Antonio Brown move was the biggest mistake of 2019 on so many levels - money, distraction, terrible fit the team culture, NFL suspension hanging over his head, track record with Oakland and Pittsburgh, on and on.