I think the people calling DJ the best "pure LB" on the team are using the following definition of "Pure LB";
The "Pure LB" looks the part and was highly touted coming out of High School. He looks like an athlete, but lacks the necessary mental skills to be effective rushing the passer or dropping into coverage. He can occassionally find the football and make a play when unblocked and the play comes directly to him. The pure LB also has no interest in being a leader, or "field general" as that sort of thing is outside the Pure LBs Purview. The only requirement of the Pure LB is that he be athletic; actual playmaking ability, ability to read offenses, and leadership ability should not be considered.