1) From 2006-2012, we drafted precisely ONE OLB. We all know who that "one" was too. That's absolutely unheard of for 3-4 defenses. I posted it in another thread, but teams like the Steelers and Niners were drafting one nearly EVERY year.
2) From 2006-2012, only three teams in the NFL have not had a double digit sacker -- the Bucs, Cards, and you guessed it, the Jets. It shouldn't come as any surprise given the first point.
3) While this class lacks the elite rusher at the top a la Von Miller/Aldon Smith, it does offer a plethora of first round pass rusher talent. This wasn't the case in the past few drafts. The only players worthy of a first round pick were top 10 caliber players. It just so happens that we weren't picking anywhere close to the top 10 in those years.
Guys like Moore, Jones, and Mingo would be able to make an immediate impact. I personally think Moore is the best fit for Rex's defense.
4) I don't know where your "OLBs drift into their 2nd/3rd teams and d-line do not" narrative is going.
4-3 ends like Jared Allen, Julius Peppers, and Mario Williams are on their second teams. I thought that only happened to OLBs? See, it goes both ways.
The reason why edge rushers bounce around are because they command enormous salaries; in fact, after QBs, edge rushers are paid the most. If a team doesn't view the edge rusher as one of their three or four core players, they let him go because they know on the open market someone will overpay for his services.
Watch it happen this year with Paul Kruger and Anthony Spencer, two guys who are great complementary edge rushers who will get paid as a premier pass rusher on a new team. It has nothing to do with them being 3-4 OLBs. And 4-3 ends like Cliff Avril and Michael Bennett will likely find new homes because their respective teams have to shell out big money to people further ahead in line (Suh/Mega/Stafford in Lions case and VJax/Nicks/Freeman in Bucs case).
Those crudy OLBs we had last year -- Thomas and Pace -- COMBINED for the same amount of sacks as Coples, an interior lineman playing ~50% of the snaps. I'd hesitate to call what Pace/Thomas put up as "numbers."
Sure, you don't need a stud at the position, but you at least need a guy who can win a one on one. Based on last year's game tape and the stat line, I would easily say we lacked that dimension.