1) Defensive Production
Is he great at coming up in run support? No. He is a high effort guy but doesn't have the mass. He runs around blocks and makes a lot of tackles downfield. He has gotten better at actually getting runners to the ground instead of just slowing them down until someone can finish them off.
Is he great at coverage? No. He is solid at coming up to defend checkdowns and screens (the single biggest impact in my mind for the Pats game). If he is downfield in coverage it is likely a mismatch.
I don't understand a lot of your observations on Leonhard. Regarding run support, it's actually one of the things he's quite good at. There were times he missed tackles last season, but remember he had a broken thumb and played with a cast. He was tackling with one arm and whatever part of his body he could use at times. He consistently takes good angles to the ball, and was tied for third on the team in tackles. He knows how to find his way to where the ball is for a team with one of the best run defenses in the league.
As for coverage, I think you're off base. There aren't many safeties that are good in down-field coverage. If they were, they'd probably be corners. Chung is pretty good in coverage for a safety, but even against an undrafted rookie free agent like Blair White, he'll get consistently burned. Leonhard does a decent enough job on the short stuff, and has a reputation as a real hard hitter back there despite his size. He shouldn't be covering a lot of guys deep very frequently, just like most safeties don't.
2) Special Teams Production
I can't believe this point even has to be argued. He has shown more reliable hands this year, but he is hardly a major threat on punt returns. I remember 2 good returns opening weekend because it was killing me how the Ravens punter outkicked his coverage. In the games I've seen since, I can't remember a time when it looked like he would break one (certainly not in the earlier Pats game). I obviously haven't seen all of his returns but he has looked very ordinary.
Again, I have no idea where you get this from. He's always been a good punt returner, even in college where he set the Big 10 career record (though he's no longer the record-holder).
If you look at guys with at least 1 punt return per game, he's in the top 10 with a healthy 11.3 average. That's better than every Patriot except Edelman, and almost 4 yards better than the other Jet returner (Wilson).
While his longest return has only been 32 yards, 4 of his 21 returns have gone for 20+ yards, tied for 2nd-most in that category behind only Devin Hester's 6. He may not be scoring touchdowns for them, but he has given them good field position consistently and broken solid returns at a higher rate than most returners, plus he has a long history of being a good returner.
3) Leadership
Impossible to know outside that locker room and hard to quantify. I compared him to James Sanders in his ability to direct the secondary and it seemed to approximate his defensive production (per snap since Sanders isn't alway full-time). Since then people have compared him to Rodney (which is beyond silly) and Meriweather (no where near his coverage skills).
I can only assume this was done because people believe his presence is critical to keeping the defense together...like Rodney in 2004. That may be, but my question is why is that level of coordination needed for this defense? He knows Ryan's defense by heart? Shouldn't they all by this point. They are all veterans and Scott came over from Baltimore as well. Three linebackers are over 30 and the other is supposedly a top ILB in his 4th year. Even the DL (with younger players but still with a couple years experience) has Ellis to provide leadership.
You're saying his leadership is impossible to know outside of the locker room and hard to quantify, but then you go on to downplay it anyways. In this instance, I'd just refer to the Jets players and coaches, who all call it a huge loss.
If losing Leonhard throws this Jets team off to any significant degree, that is an indictment of their team building.
The guy behind him is obviously less talented. It's natural to expect an adjustment period as well, and that you won't be able to do all of the things you want to do. Polamalu's injury last year is another example of how an injury can change what a defense is capable of, and it's hardly an indictment of their team that they don't have another Pro Bowl safety stashed away.
Someone else will get time, get an opportunity, and maybe make some plays. But it definitely limits them in some ways and changes some of the things they can do. We won't know the full impact of it for a few weeks, and neither will the Jets as they try to adjust.
As for Leonhard, he is a really under-rated player in the league, but not to the Jets. You hate to see anyone get injured and I hope he gets better. I think Rex will want him back next year unlike the way things went with Leon Washington this year.
