So let's examine the contract:
3 Years, $15 mil $9 mil guaranteed. For easy math, let's say he makes $5 mil/year (BTW, worst case scenario, this contract is easy to get out of in 2017 or 2018).
Bethel is arguably one of the best special teams players in the NFL (3x Pro Bowl and 2x All-Pro). So what value alone do you give him just for that part of the game? Many special teams "aces" who aren't starters on offense or defense make ~ $1.5 mil/year in their second contracts. With Bethel being as great as he is, I'd say his value is closer to $2 mil/year alone as a special teams ace and captain.
Now that leaves $3 mil/year as a starting #2 CB, which is about the going rate +/- as a #2 CB. Put in perspective, Jarraud powers was making $3.5 mil/year as a #2 CB last season.
All together, if you only count Bethel as a CB, his contract is ranked #38 in total value; however, his value is so much more to the team because he's so good at his responsibility as a special teams player.
Does Bethel need to get better as a CB? Sure, especially since he's going to be targeted a ton w/ PP21 on the other side, but he has the size and athleticism to at least be a decent #2 option.
Early nominee for the 2016 "Stevie Williams Training Camp Champ" trophy.
He's raw and is still learning the position. He's made plays, but has also been torched several times. If you want to put all of your chips into a raw rookie who's had four total TC practices in his NFL career, by all means, go for it.