Zach is clearly going down hill and he's very mediocre in this defense. When you watch a lot of NFL games you see a ton of LB's making big plays - the kind Zach used to make - and I'd put 10 MLB's ahead of him right now. He is slow in pass coverage and he cannot blitz. His style of play is not fitting the majority of NFL defenses. He doesn't, as coaches like to say, "play downhill" anymore.
JT is also losing a bit of quickness. That quickness has cost him dearly. He has one rush - speed rush from the outside. He can put an occasional move on a lineman, but, the good pass blocking OT's handle him most of the game. They either stop him straight up or, if he rushes to the outside they just push him too deep - outside the pocket.
These two have been the face of what is good for the Dolphins for the past decade, but they are down hill. They are no longer the type who can carry a team. If JT is on a team where the rest of the defense is stellar - he could still do some damage for a few more years. But, these two could easily be replaced in a year or two.
We need LB's that are big, fast, and can penetrate behind the line of scrimmage. It's not just about making a tackle for a 3 yard gain. The top defenses today are blowing up offenses on key plays. Even then, teams are going to score points.
This is not dissing Zach. I've loved to watch him play, but he's just not making the game breaking plays he used to. He's solid, but we need a wrecking crew on defense that creates turnovers.