Roy Williams plays on special teams, I don't see what the big deal is.
Because Roy ... nor Darren Woodson, nor Dexter Coakley or whoever else you want to throw out there .... were not playing the gunner position. The one where you're lined up far to the outside and have two blockers knocking you around 10 yards out of bounds and you have to find a way to loop back inside to make a play, expends a heck of a lot of energy. I promise you if an opponent sees a Davis out there at FS after playing the gunner position the previous punt coverage they are going to throw deep on the first play because they know he'll be gassed.
If Davis plays on all 4 special teams packages he's seeing around 25-30 snaps a game. If he gets in on nickel and dime packages on the defense you're looking at another 25-30 snaps per game.
I hardly see how Davis would be underutilized at 60 snaps a game.
Unless you're one of those people who consider special teams snaps to be meaningless ... which, of course, I know a lot of people do.
(And yes, it probably is harder to find a great special team gunner than it is to find a average free safety)