Easy answer would be to keep both...just don't know how easy it would actually be. Dez was drafted a Cowboy, and is simply one of the most productive offensive weapons in the league. Hardy might be a 1-year rental, who was available & financially feasible, only because of his legal issues. Between 2012 & 2013, he produced the 3rd most sacks in the league. Both command extra attention from the opposition...which benefits others.
As far as the Pats, they don't have an 'elite' pass rusher, but have a few solid/versatile guys in their front 7 that can create pressure/get home. LB Hightower (6 sacks), LB Collins (4 sacks), DE Jones (6 sacks), DE/LB Ninkovich (8 sacks). And they've now added Jabaal Sheard to the mix. They also had elite secondary players in Revis & McCourty. They do have an elite pass catcher in Gronk.
Seattle has run the ball over 50% of the time. They traded for an elite pass catcher in Graham & signed another solid DL player in NT Ahtyba Rubin. They utilize a rotation of pass rushers...and like the Pats, none of them had over 8 sacks.
I think Crawford & Lawrence will continue to ascend, and hopefully they keep adding pieces to that when they have the opportunity...particularly via the draft. Hardy is signed to a 1-year deal...and IIRC, Mincey has 1-year left on his deal.
As far as Hardy this season, he could potentially provide Marinelli with a very similar DL to what he had in Chicago in 2012, when the Bears finished with a league leading 44 takeaways...were 3rd in scoring D...top 10 vs. the Run & Pass.
Bears 2012 DL & their sacks: Idonije/Wootton (both had 7 sacks), Melton (7 sacks), Paea (2.5), Peppers (11.5)
Boys 2015 DL: Lawrence/Mincey, Crawford, Brent, Hardy