He may be the best player in the draft, but unless he is a full time WR for the Pats, he is a luxury pick that the Pats cannot afford to make. He cannot play both ways full time in the NFL. He will either be a full time CB and a part time WR (which where most people think he will end up) or a full time WR who can play CB in certain packages.
Again, having two elite CBs does the Pats nothing if they do not have a true #1 WR, a franchise tackle, or a pass rush. What good is it to have either Gonzalez or Hunter locked on another team's #2 WR if Maye is constantly running for his life or no one is getting open?
If Hunter is the best player in the draft and he falls to the Pats, the Pats will get a lot of potential trade partners driving up the compensation for him. For a team like the Pats, multiple high draft picks is more important than a player like Hunter unless they think he will be an elite full time WR.