Effort and accountability. They weren't the most talented defenses, but you could never question his defenses for giving a balls-to-the-wall maximum effort all the time. Many times that alone made up for a disparity or talent was concerned.
One of the biggest issues with this defense (outside of a general lack of game plan adaptation and adjustment by Tuiaki) is that players don't seem to consistently exhibit the same degree of effort I play with the same degree of accountability that they did under the previous head coach. I see that as more of a reflection of the head coach than a coordinator in this case.
Improve the game planning and in game of Justin by coaches, and improve the effort and accountability that players since, and this defense would perform substantially better. it would be a lot closer to 6-2 than 2-6 in that case.