I haven't seen this raised with relation to why our defense is so bad, but here it is: we effectively have 6 offensive and 4 defensive coaches. Really.
Rodriguez has spent almost all his time with the offense. On top of that you have Dews (WR), Frey (O-line), Smith (Qbs), Jackson (Rbs) and Magee (O-coordinator, TEs and Slots).
On defense we've got Tall (D-line), Braithwaite (safeties), Gibson (corners? and special teams) and Robinson (D-coordinator and LBs).
So yeah, we have 50% more coaches devoted to offense. One effect is both Gibson and Robinson double up while the offensive coaches are more specialized. Another is that simple math dictates defensive players get less coaching per player than offensive players. I don't know what to say besides derpity derpity derp derp doo. FML.
EDIT: I've been doing more research to figure out exactly what is common practice and how much different arrangements are correlated with a relatively stronger defense or offense. I'll be making this into a diary in the coming days.