[revised with much better figures as suggested by tinley]
I posted this elsewhere, but might as well make a fan post about it. There is a fantasy going around out there that Coples suddenly became a beast in the 2nd half of the year...as a pass rusher. This was probably born from people looking at the last two (meaningless games) and projecting backwards. In the last half of the year Coples was almost exactly average. The combined league PRP (which counts hits and hurries weighted, and sacks, per rush) among high snap 3-4 OLBers was 10.22. In the last 8 games Coples' average was 10.29 (whew, it was close). This is far from exceptional, even though it was an improvement over "dreadful" from earlier in the year. Besides the fact his best games came when standings didn't really matter any longer, most of his pressures during this time came because he was stunting inside over and over, taking advantage of our inside strength, and giving up on the outside rush which he is horrible at. Almost zero of his pressure came from an outside rush, I watched him very closely in film in the second half. As I've pointed out before if you can't rush from the outside, you can't play the position at a high level. Teams started taking advantage of his stunts inside, running off his edge time and again, while he dove inside the tackle, or looped around. A big part of a OLB is to seal the edge. The problem is, if he stays outside he can't get to the passer, he just gets stood up or pushed out of the play. He basically has to abandon his post to rush the passer. Add in the fact that he doesn't doesn't have an elite motor (to be kind about it), and we are talking about a guy who not only is out of position, he's taking plays off out of position.
Below are all his PRP stats per game from 2013. The red line shows league average. The shaded red area shows where the top 3 pass rushing OLBers AVERAGED for the year, over 14. Hughes, Dumervil and Houston. These guys were "exceptional". Coples was not even close to great. He was league average in the last 8 games, and I suggest he was so only because he stopped protecting the edge consistently. It's a big problem. He basically was turned into a stunting inside pass rusher, and not an OLBer edge rusher.
Maybe Rex finds a way to creatively keep Coples diving inside from the OLBer position, and still protect the edge with other players, but this involves a straining of the defense to hide a major weakness that the Jets themselves have created. I wouldn't mind a Coples trade, if they don't figure out a way to get him back inside as a matter of position. Maybe Rex (who never drafts an edge rusher) and Rod Graves (who didn't draft them either) decide to switch course and give us someone who can handle the position and grow with the defense. But I suspect that isn't going to be the case. Rex probably wants to prove everyone wrong about Coples and will bend over backwards to make it happen. And Coples will progress just enough to keep fans thinking that one or two very good games in 2014 means that he's ready to break out in 2015...
addendum...tinley had a good question in comments, what was Pace's PRP in comparison to Coples? So I repost the year's performance of both players below (Pace purple, Coples still blue). It is important to note that Pace got his pressures with far fewer rushes than Coples, he was very effective when he rushed, at least as far as Jets go. To illustrate, Coples rushed the passer 95.1% of the time on passing plays he was on the field for, whereas Pace rushed the passer in only 56.1% of the time for pass plays he was on the field for. The rest of the time Pace was in coverage. This points to a hidden importance of Pace to the team (for haters of Pace). He helped make up for the inability of Coples to play in space and drop into coverage. This was a further drawback to Coples because the offense knew already how to attack, and where the coverage drop was going to be. For a team that had huge problems in the shorter passing game (as neither inside linebacker could cover), this weakness of Coples's worsened an already existing fissure in the defense.
I also add in Barnes' 5 games (green) because people also have a much inflated picture of how important Barnes was to the pass rush. As you can see, he was really no better than an average pass rusher in production (though he likely was a nice piece to have). Basically once Barnes left, Pace's game took off.