I run the CRMS Kayak program. I have had 34 LL kayaks. The only cracking problems that I have personally encountered are in the early models where they did not have a washer under the seat bolt on the first years of the lil Joe, Hoss, Airhead era. That was 1 Joe, 1 hoss, three airheads( lot of torque on a small spot). The only Jefe that I personally know that cracked had been drug over the sierra and back and worn thin.
The nature of molding plastic can lead to thin spots. It seems like a balance between putting enough plastic powder in the mold to be strong and putting so much in that it is a brick. If you search this forum you will find some complaint about every companies' plastic and people who swear by them. My personal experience with LL plastic is that it is solid.
The Jefe got me back into creeking after years of not feeling comfortable in a boat. Stupid Gradient. I think you'll find lots of others had similar experience.
liquidlogic also does extensive boat testing.