The Ravens defensive line is usually thought of as the deepest unit on the team. However, the late season slump in the 2016 season seems to speak against this. The Ravens mostly ran a five man rotation. Willie Henry, Carl Davis, Kapron Lewis-Moore and Bronson Kaufusi were non-factors.
Lawrence Guy is a free agent. While he provided solid, if unspectacular play for the Ravens, having a player like Calais Campbell (if he hits the market) could add first step explosiveness that the Ravens do not have on the interior. Baltimore's pass rush struggled for most of the season. Most of the blame has gone to the outside linebackers but having players that can rush the quarterback on early downs from base defense would help make the pass rush more consistent, and not overly reliant on sub packages.
Calais Campbell has been an elite player for close to five years. His sack numbers aren't on the level of J.J Watt, who is the standard for all five techniques, but nevertheless his numbers reflect his disruption, as he has consistently ranked in the Pro Football Focus' top defensive linemen.
If Campbell is looking to make monetary sacrifices to get a chance to compete for a Super Bowl, the Ravens have the option to shed salary in the more mediocre players on he roster to bring in an elite talent.