Sixth best? BS. I'd say only Willis and Bowman are better for sure.
I actually like JL (if not love him), so that is more of a testament to how good the NFC West defenses are. SEA and SF were 1-2 in the NFL, I think, an ARI might have been around 6?
There are different ways to look at it, and age would factor into it if were GMs actually building a real team.
Bobby Wagner may have made the Pro Bowl in his rookie season, he was one of the top rookies LBs (and defensive players overall) in 2012 with Luke Kuechly and Lavonte David. Statistically he didn't seem to make as big an impact last year, and when we think about their defense, it does tend to be about the Pro Bowl stacked secondary (Thomas, Sherman, Chancellor), but Wagner plays a key role in the best defense in the league. I don't think the fact that he is faster and more athletic than Laurinaitis could be in dispute. JL may be smarter and have better instincts (not even sure about that), but Wagner's youth and superior range him significantly more upside (in run support and coverage), IMO, if in fact he isn't more talented already.
In ARI, Daryl Washington had some off field problems and was suspended for the first month of the 2013 season, and had a somewhat quiet season, but in 2012 he was one of the best LBs in the league, and pretty sure he was a Pro Bowler. He runs and covers like a safety, was a prolific tackler (top 3 that year?) and also had something like 8 sacks, not sure if that was near a record for an ILB/MLB? WIh Dansby, age comes into play. I'd rather have JL because he is like 32-33 (?). But if we are justtalking straight up who is more talented, I don't think it is close. Dansby was a former Card who went to MIA in free agency around 2010, and returned in 2013. I don't know if he made the Pro Bowl (kind of tough with how stacked the NFC in general and NFC West specifically is), but he easily had the stats to do so. Pretty sure he was among the leaders in tackles, and had some big plays, too. Dansby is a gifted athlete that was a nationally recruited, top 20-30 WR for Auburn, was converted to safety (and retained the kind of coverage ability and hands we assciate with that position) , and blew up to LB size, where he may hve played outside and inside. Ogletree has a similar resume and career arc, as a former safety that played LB inside and outside at Georgia, and we can see the tantalizing athleticism and raw coverage potential that could make him a future star and Pro Bowler. A player with if possible an even more impressive background as a freakish athlete with positional versatility (I remember Carnell Lake played LB at UCLA, and safety for PIT in the NFL, even filling in at a high level as a CB when there were injuries) is Pats rookie second rounder Jamie Collins, also a former safety who played outside and MLB, and even DE his last year. Despite not playing much in the regular season, he looked like an emerging star in the playoffs. I think he broke the Combine broad jump record (around 11'7", previously held by Calvin Johnson, one of the freakiest of the freaky himself :^) ).
I started a thread at another site, and compared STL to SEA in this respect. And BTW, guys like Chris Long and JL are respected team leaders, so even if they are slipping a little from their prime, or if their skills were to slowly erode, they probably aren't going anywhere for a few years. But when you lock players into $10 million per year contracts, you kind of become joined at the hip for a while. SEA has the constant competition philosophy which he brought from USC, so if JL had been there, I'm not sure he would have the attitude that he is our guy from the next half decade, or would he recognize that he is good but not great at a very important positon, and look to upgrade him? But, maybe like Bradford on offense, who will probably never be Manning, Brady, Brees or Rodgers, but has the upside to crack the top 10, and we can win with by surrounding him with more talent, we can better the defense around JL (we already did with Ogletree, Quinn elevated his game and took a giant step forward in his evolution, Brockers is a future stud, the next step imo is to upgrade the secondary with a FS and more CB talent/depth).