1. The Pats signed Carlton but passed on the available FSs.
2. It has been suggested that Mapu could play FS, but he has not been great at that.
3. Hunter is great with the ball in front of him, very good at zone coverage which is similar to FS.
4. For running downs Mapu might be better at FS because he is better at tackling.
5. On passing downs Hunter might be a better choice at FS because of his instincts, quickness, speed, and veratility (like you noted).
6. Only playing FS on passing downs would limit Hunter's snaps on defense when he is playing WR on offense.
7. Hunter can play single high FS with Carlton and Gonzo as the outside corners working on islands, or drop into 2-high, or 3-high. Hunter can also drop down to cover the slot or a TE on Zero blitzes.
If the Pats signed a FS in FA, I would doubt they are considering Hunter at safety, but since they didn't I doubt Mapu is our FS on passing downs. Hunter would be a logical choice at FS if the Pats draft him.
The Pats did try to sign Godwin as a WR, so maybe they are not thinking about drafting Hunter and will pick a LT candidate and I am completely wrong - LOL.