Yes, the defense was worse than the Offense for most of the year. However, played very well against Miami and the Jets. Giving up only 13 points over those two games. Poor tackling, I think, is an NFL problem not just a Bills problem.
Marv wasting picks on D? I don't get that. All of the rooks played very well for their FIRST year in the NFL. If anything, look at the playing time they received. This defense will be much, MUCH better next year with everyone having that one year under their belt.