Yes, the Lerners are to blame for the "dark years" after they took over in 2006, but I think that the blame has to be measured.
First, as we all know they took over a team that had been looted and pillaged by the other 29 owners with Bud's assent.
Secondly, although the Lerners are incredibly savvy business people, they were novices in the baseball world. We all know JimBo is a slick talker. I think he convinced them that he had some sort of magic eye for talent and could spot the diamonds in the rough, and could build them a contending baseball team on the cheap. We all like a bargain so it's understandable that they'd want to believe that. Additionally, they did have a supposed baseball expert in the group in Stan Kasten, who was forced on them by Bud to provide some baseball experience for the ownership group. I never heard rumors to the effect that Kasten ever stood up and told them that JB was all talk and very little talent.
So they inherited a team that was horrible to begin with, lucked out into 2005 season that was fluke for the talent on hand but probably served only to disguise the true lack of talent, had a slick-talking GM in JB, and a supposed baseball "expert" in Stan Kasten who failed to tell them that everyone in baseball knew that JB was full of it. I give them credit for finally figuring it out (thanks in large part to the DR baseball scandal) and eventually clearing out both JB and Kasten to make room for better FO talent.
And I love that we're going for character guys as well as talent guys - no Elijah Dukes types in that clubhouse. I believe that's a big factor in how well this team seems to have gelled this year - no clubhouse cancer types to interfere with team chemistry.